diff --git a/server/src/matrix/bot.rs b/server/src/matrix/bot.rs
index f392044..786de48 100644
--- a/server/src/matrix/bot.rs
+++ b/server/src/matrix/bot.rs
@@ -888,6 +888,46 @@ async fn on_room_message(
         return;
     }
 
+    // Check for the start command, which requires async agent ops and cannot
+    // be handled by the sync command registry.
+    if let Some(start_cmd) = super::start::extract_start_command(
+        &user_message,
+        &ctx.bot_name,
+        ctx.bot_user_id.as_str(),
+    ) {
+        let response = match start_cmd {
+            super::start::StartCommand::Start {
+                story_number,
+                agent_hint,
+            } => {
+                slog!(
+                    "[matrix-bot] Handling start command from {sender}: story {story_number} agent={agent_hint:?}"
+                );
+                super::start::handle_start(
+                    &ctx.bot_name,
+                    &story_number,
+                    agent_hint.as_deref(),
+                    &ctx.project_root,
+                    &ctx.agents,
+                )
+                .await
+            }
+            super::start::StartCommand::BadArgs => {
+                format!(
+                    "Usage: `{} start <number>` or `{} start <number> opus`",
+                    ctx.bot_name, ctx.bot_name
+                )
+            }
+        };
+        let html = markdown_to_html(&response);
+        if let Ok(msg_id) = ctx.transport.send_message(&room_id_str, &response, &html).await
+            && let Ok(event_id) = msg_id.parse()
+        {
+            ctx.bot_sent_event_ids.lock().await.insert(event_id);
+        }
+        return;
+    }
+
     // Spawn a separate task so the Matrix sync loop is not blocked while we
     // wait for the LLM response (which can take several seconds).
     tokio::spawn(async move {
diff --git a/server/src/matrix/commands/mod.rs b/server/src/matrix/commands/mod.rs
index 51ab0fc..23cdf1a 100644
--- a/server/src/matrix/commands/mod.rs
+++ b/server/src/matrix/commands/mod.rs
@@ -120,6 +120,11 @@ pub fn commands() -> &'static [BotCommand] {
             description: "Show implementation summary for a merged story: `overview <number>`",
             handler: overview::handle_overview,
         },
+        BotCommand {
+            name: "start",
+            description: "Start a coder on a story: `start <number>` or `start <number> opus`",
+            handler: handle_start_fallback,
+        },
         BotCommand {
             name: "delete",
             description: "Remove a work item from the pipeline: `delete <number>`",
@@ -221,6 +226,16 @@ fn handle_htop_fallback(_ctx: &CommandContext) -> Option<String> {
     None
 }
 
+/// Fallback handler for the `start` command when it is not intercepted by
+/// the async handler in `on_room_message`.  In practice this is never called —
+/// start is detected and handled before `try_handle_command` is invoked.
+/// The entry exists in the registry only so `help` lists it.
+///
+/// Returns `None` to prevent the LLM from receiving "start" as a prompt.
+fn handle_start_fallback(_ctx: &CommandContext) -> Option<String> {
+    None
+}
+
 /// Fallback handler for the `delete` command when it is not intercepted by
 /// the async handler in `on_room_message`.  In practice this is never called —
 /// delete is detected and handled before `try_handle_command` is invoked.
diff --git a/server/src/matrix/mod.rs b/server/src/matrix/mod.rs
index 7231ce7..433adfa 100644
--- a/server/src/matrix/mod.rs
+++ b/server/src/matrix/mod.rs
@@ -20,6 +20,7 @@ pub mod commands;
 mod config;
 pub mod delete;
 pub mod htop;
+pub mod start;
 pub mod notifications;
 pub mod transport_impl;
 
diff --git a/server/src/matrix/start.rs b/server/src/matrix/start.rs
new file mode 100644
index 0000000..30a18ed
--- /dev/null
+++ b/server/src/matrix/start.rs
@@ -0,0 +1,349 @@
+//! Start command: start a coder agent on a story.
+//!
+//! `{bot_name} start {number}` finds the story by number, selects the default
+//! coder agent, and starts it.
+//!
+//! `{bot_name} start {number} opus` starts `coder-opus` (or any agent whose
+//! name ends with the supplied hint, e.g. `coder-{hint}`).
+
+use crate::agents::AgentPool;
+use std::path::Path;
+
+/// A parsed start command from a Matrix message body.
+#[derive(Debug, PartialEq)]
+pub enum StartCommand {
+    /// Start the story with this number using the (optional) agent hint.
+    Start {
+        story_number: String,
+        /// Optional agent name hint (e.g. `"opus"` → resolved to `"coder-opus"`).
+        agent_hint: Option<String>,
+    },
+    /// The user typed `start` but without a valid numeric argument.
+    BadArgs,
+}
+
+/// Parse a start command from a raw Matrix message body.
+///
+/// Strips the bot mention prefix and checks whether the first word is `start`.
+/// Returns `None` when the message is not a start command at all.
+pub fn extract_start_command(
+    message: &str,
+    bot_name: &str,
+    bot_user_id: &str,
+) -> Option<StartCommand> {
+    let stripped = strip_mention(message, bot_name, bot_user_id);
+    let trimmed = stripped
+        .trim()
+        .trim_start_matches(|c: char| !c.is_alphanumeric());
+
+    let (cmd, args) = match trimmed.split_once(char::is_whitespace) {
+        Some((c, a)) => (c, a.trim()),
+        None => (trimmed, ""),
+    };
+
+    if !cmd.eq_ignore_ascii_case("start") {
+        return None;
+    }
+
+    // Split args into story number and optional agent hint.
+    let (number_str, hint_str) = match args.split_once(char::is_whitespace) {
+        Some((n, h)) => (n.trim(), h.trim()),
+        None => (args, ""),
+    };
+
+    if !number_str.is_empty() && number_str.chars().all(|c| c.is_ascii_digit()) {
+        let agent_hint = if hint_str.is_empty() {
+            None
+        } else {
+            Some(hint_str.to_string())
+        };
+        Some(StartCommand::Start {
+            story_number: number_str.to_string(),
+            agent_hint,
+        })
+    } else {
+        Some(StartCommand::BadArgs)
+    }
+}
+
+/// Handle a start command asynchronously.
+///
+/// Finds the work item by `story_number` across all pipeline stages, resolves
+/// the agent name from `agent_hint`, and calls `agents.start_agent`.
+/// Returns a markdown-formatted response string.
+pub async fn handle_start(
+    bot_name: &str,
+    story_number: &str,
+    agent_hint: Option<&str>,
+    project_root: &Path,
+    agents: &AgentPool,
+) -> String {
+    const STAGES: &[&str] = &[
+        "1_backlog",
+        "2_current",
+        "3_qa",
+        "4_merge",
+        "5_done",
+        "6_archived",
+    ];
+
+    // Find the story file across all pipeline stages.
+    let mut found: Option<(std::path::PathBuf, String)> = None; // (path, story_id)
+    'outer: for stage in STAGES {
+        let dir = project_root.join(".story_kit").join("work").join(stage);
+        if !dir.exists() {
+            continue;
+        }
+        if let Ok(entries) = std::fs::read_dir(&dir) {
+            for entry in entries.flatten() {
+                let path = entry.path();
+                if path.extension().and_then(|e| e.to_str()) != Some("md") {
+                    continue;
+                }
+                if let Some(stem) = path
+                    .file_stem()
+                    .and_then(|s| s.to_str())
+                    .map(|s| s.to_string())
+                {
+                    let file_num = stem
+                        .split('_')
+                        .next()
+                        .filter(|s| !s.is_empty() && s.chars().all(|c| c.is_ascii_digit()))
+                        .unwrap_or("")
+                        .to_string();
+                    if file_num == story_number {
+                        found = Some((path, stem));
+                        break 'outer;
+                    }
+                }
+            }
+        }
+    }
+
+    let (path, story_id) = match found {
+        Some(f) => f,
+        None => {
+            return format!(
+                "No story, bug, or spike with number **{story_number}** found."
+            );
+        }
+    };
+
+    // Read the human-readable name from front matter for the response.
+    let story_name = std::fs::read_to_string(&path)
+        .ok()
+        .and_then(|contents| {
+            crate::io::story_metadata::parse_front_matter(&contents)
+                .ok()
+                .and_then(|m| m.name)
+        })
+        .unwrap_or_else(|| story_id.clone());
+
+    // Resolve agent name: try "coder-{hint}" first, then the hint as-is.
+    let resolved_agent: Option<String> = agent_hint.map(|hint| {
+        let with_prefix = format!("coder-{hint}");
+        // We'll pass the prefixed form; start_agent validates against config.
+        // If coder- prefix is already there, don't double-prefix.
+        if hint.starts_with("coder-") {
+            hint.to_string()
+        } else {
+            with_prefix
+        }
+    });
+
+    crate::slog!(
+        "[matrix-bot] start command: starting story {story_id} with agent={resolved_agent:?} (bot={bot_name})"
+    );
+
+    match agents
+        .start_agent(project_root, &story_id, resolved_agent.as_deref(), None)
+        .await
+    {
+        Ok(info) => {
+            format!(
+                "Started **{story_name}** with agent **{}**.",
+                info.agent_name
+            )
+        }
+        Err(e) => {
+            format!("Failed to start **{story_name}**: {e}")
+        }
+    }
+}
+
+/// Strip the bot mention prefix from a raw Matrix message body.
+///
+/// Mirrors the logic in `commands::strip_bot_mention` and `delete::strip_mention`.
+fn strip_mention<'a>(message: &'a str, bot_name: &str, bot_user_id: &str) -> &'a str {
+    let trimmed = message.trim();
+    if let Some(rest) = strip_prefix_ci(trimmed, bot_user_id) {
+        return rest;
+    }
+    if let Some(localpart) = bot_user_id.split(':').next()
+        && let Some(rest) = strip_prefix_ci(trimmed, localpart)
+    {
+        return rest;
+    }
+    if let Some(rest) = strip_prefix_ci(trimmed, bot_name) {
+        return rest;
+    }
+    trimmed
+}
+
+fn strip_prefix_ci<'a>(text: &'a str, prefix: &str) -> Option<&'a str> {
+    if text.len() < prefix.len() {
+        return None;
+    }
+    if !text[..prefix.len()].eq_ignore_ascii_case(prefix) {
+        return None;
+    }
+    let rest = &text[prefix.len()..];
+    match rest.chars().next() {
+        None => Some(rest),
+        Some(c) if c.is_alphanumeric() || c == '-' || c == '_' => None,
+        _ => Some(rest),
+    }
+}
+
+// ---------------------------------------------------------------------------
+// Tests
+// ---------------------------------------------------------------------------
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // -- extract_start_command -----------------------------------------------
+
+    #[test]
+    fn extract_with_full_user_id() {
+        let cmd =
+            extract_start_command("@timmy:home.local start 331", "Timmy", "@timmy:home.local");
+        assert_eq!(
+            cmd,
+            Some(StartCommand::Start {
+                story_number: "331".to_string(),
+                agent_hint: None
+            })
+        );
+    }
+
+    #[test]
+    fn extract_with_display_name() {
+        let cmd = extract_start_command("Timmy start 42", "Timmy", "@timmy:home.local");
+        assert_eq!(
+            cmd,
+            Some(StartCommand::Start {
+                story_number: "42".to_string(),
+                agent_hint: None
+            })
+        );
+    }
+
+    #[test]
+    fn extract_with_localpart() {
+        let cmd = extract_start_command("@timmy start 7", "Timmy", "@timmy:home.local");
+        assert_eq!(
+            cmd,
+            Some(StartCommand::Start {
+                story_number: "7".to_string(),
+                agent_hint: None
+            })
+        );
+    }
+
+    #[test]
+    fn extract_with_agent_hint() {
+        let cmd = extract_start_command("Timmy start 331 opus", "Timmy", "@timmy:home.local");
+        assert_eq!(
+            cmd,
+            Some(StartCommand::Start {
+                story_number: "331".to_string(),
+                agent_hint: Some("opus".to_string())
+            })
+        );
+    }
+
+    #[test]
+    fn extract_case_insensitive_command() {
+        let cmd = extract_start_command("Timmy START 99", "Timmy", "@timmy:home.local");
+        assert_eq!(
+            cmd,
+            Some(StartCommand::Start {
+                story_number: "99".to_string(),
+                agent_hint: None
+            })
+        );
+    }
+
+    #[test]
+    fn extract_no_args_is_bad_args() {
+        let cmd = extract_start_command("Timmy start", "Timmy", "@timmy:home.local");
+        assert_eq!(cmd, Some(StartCommand::BadArgs));
+    }
+
+    #[test]
+    fn extract_non_numeric_arg_is_bad_args() {
+        let cmd = extract_start_command("Timmy start foo", "Timmy", "@timmy:home.local");
+        assert_eq!(cmd, Some(StartCommand::BadArgs));
+    }
+
+    #[test]
+    fn extract_non_start_command_returns_none() {
+        let cmd = extract_start_command("Timmy help", "Timmy", "@timmy:home.local");
+        assert_eq!(cmd, None);
+    }
+
+    // -- handle_start (integration-style, uses temp filesystem) --------------
+
+    #[tokio::test]
+    async fn handle_start_returns_not_found_for_unknown_number() {
+        let tmp = tempfile::tempdir().unwrap();
+        let project_root = tmp.path();
+        for stage in &["1_backlog", "2_current", "3_qa", "4_merge", "5_done", "6_archived"] {
+            std::fs::create_dir_all(project_root.join(".story_kit").join("work").join(stage))
+                .unwrap();
+        }
+        let agents = std::sync::Arc::new(crate::agents::AgentPool::new_test(3000));
+        let response = handle_start("Timmy", "999", None, project_root, &agents).await;
+        assert!(
+            response.contains("No story") && response.contains("999"),
+            "unexpected response: {response}"
+        );
+    }
+
+    #[test]
+    fn start_command_is_registered() {
+        use crate::matrix::commands::commands;
+        let found = commands().iter().any(|c| c.name == "start");
+        assert!(found, "start command must be in the registry");
+    }
+
+    #[test]
+    fn start_command_appears_in_help() {
+        let result = crate::matrix::commands::tests::try_cmd_addressed(
+            "Timmy",
+            "@timmy:homeserver.local",
+            "@timmy help",
+        );
+        let output = result.unwrap();
+        assert!(
+            output.contains("start"),
+            "help should list start command: {output}"
+        );
+    }
+
+    #[test]
+    fn start_command_falls_through_to_none_in_registry() {
+        // The start handler in the registry returns None (handled async in bot.rs).
+        let result = crate::matrix::commands::tests::try_cmd_addressed(
+            "Timmy",
+            "@timmy:homeserver.local",
+            "@timmy start 42",
+        );
+        assert!(
+            result.is_none(),
+            "start should not produce a sync response (handled async): {result:?}"
+        );
+    }
+}