diff --git a/src/app/chain/page.tsx b/src/app/chain/page.tsx
new file mode 100644
index 00000000..38c0b635
--- /dev/null
+++ b/src/app/chain/page.tsx
@@ -0,0 +1,191 @@
+"use client";
+
+import { useState } from "react";
+import { useAccount } from "wagmi";
+import { useQuery } from "@tanstack/react-query";
+import { ConnectWallet } from "../../components/ConnectWallet";
+import {
+  validateContentLength,
+  MIN_CONTENT_LENGTH,
+  MAX_CONTENT_LENGTH,
+} from "../../../lib/content";
+import { supabase, type Storyline } from "../../../lib/supabase";
+import { useChainPlot } from "../../hooks/useChainPlot";
+import type { PublishState } from "../../hooks/usePublish";
+import Link from "next/link";
+
+const STATE_LABELS: Record<PublishState, string> = {
+  idle: "",
+  uploading: "Uploading to IPFS...",
+  confirming: "Confirm in wallet...",
+  pending: "Publishing to Base...",
+  indexing: "Indexing...",
+  published: "Published!",
+  error: "Error",
+};
+
+async function fetchWriterStorylines(address: string): Promise<Storyline[]> {
+  if (!supabase) return [];
+  const { data } = await supabase
+    .from("storylines")
+    .select("*")
+    .eq("writer_address", address.toLowerCase())
+    .eq("hidden", false)
+    .eq("sunset", false)
+    .order("block_timestamp", { ascending: false })
+    .returns<Storyline[]>();
+  return data ?? [];
+}
+
+export default function ChainPlotPage() {
+  const { address, isConnected } = useAccount();
+  const [storylineId, setStorylineId] = useState<number | null>(null);
+  const [content, setContent] = useState("");
+
+  const { data: storylines = [], isLoading: loadingStorylines } = useQuery({
+    queryKey: ["writer-active-storylines", address],
+    queryFn: () => fetchWriterStorylines(address!),
+    enabled: isConnected && !!address,
+  });
+
+  const { state, error, chainPlot, reset } = useChainPlot();
+  const { valid, charCount } = validateContentLength(content);
+  const canSubmit =
+    (state === "idle" || state === "error") &&
+    storylineId !== null &&
+    valid;
+
+  if (!isConnected) {
+    return (
+      <div className="flex min-h-screen flex-col items-center justify-center gap-4 px-6">
+        <p className="text-muted text-sm">
+          Connect your wallet to chain a plot.
+        </p>
+        <ConnectWallet />
+      </div>
+    );
+  }
+
+  if (state === "published") {
+    return (
+      <div className="flex min-h-screen flex-col items-center justify-center gap-6 px-6">
+        <h1 className="text-accent text-2xl font-bold">Plot chained!</h1>
+        <div className="flex gap-3">
+          {storylineId && (
+            <Link
+              href={`/story/${storylineId}`}
+              className="border-border text-muted hover:text-foreground rounded border px-4 py-2 text-sm transition-colors"
+            >
+              View story
+            </Link>
+          )}
+          <button
+            onClick={reset}
+            className="border-accent text-accent hover:bg-accent hover:text-background rounded border px-4 py-2 text-sm transition-colors"
+          >
+            Chain another
+          </button>
+        </div>
+      </div>
+    );
+  }
+
+  const busy = state !== "idle" && state !== "error";
+
+  return (
+    <div className="mx-auto max-w-2xl px-6 py-12">
+      <h1 className="text-accent text-2xl font-bold tracking-tight">
+        Chain Plot
+      </h1>
+
+      <form
+        onSubmit={(e) => {
+          e.preventDefault();
+          if (canSubmit) chainPlot(storylineId, content);
+        }}
+        className="mt-8 space-y-6"
+      >
+        {/* Storyline selector */}
+        <div>
+          <label className="text-foreground mb-2 block text-sm">
+            Storyline
+          </label>
+          {loadingStorylines ? (
+            <p className="text-muted text-sm">Loading storylines...</p>
+          ) : storylines.length === 0 ? (
+            <p className="text-muted text-sm">
+              No active storylines.{" "}
+              <Link href="/create" className="text-accent hover:underline">
+                Create one
+              </Link>
+            </p>
+          ) : (
+            <select
+              value={storylineId ?? ""}
+              onChange={(e) =>
+                setStorylineId(e.target.value ? Number(e.target.value) : null)
+              }
+              disabled={busy}
+              className="border-border bg-surface text-foreground w-full rounded border px-3 py-2 text-sm focus:border-accent focus:outline-none disabled:opacity-50"
+            >
+              <option value="">Select a storyline</option>
+              {storylines.map((s) => (
+                <option key={s.id} value={s.storyline_id}>
+                  {s.title} ({s.plot_count}{" "}
+                  {s.plot_count === 1 ? "plot" : "plots"})
+                </option>
+              ))}
+            </select>
+          )}
+        </div>
+
+        {/* Content */}
+        <div>
+          <label className="text-foreground mb-2 block text-sm">
+            Next Chapter
+          </label>
+          <textarea
+            value={content}
+            onChange={(e) => setContent(e.target.value)}
+            disabled={busy}
+            rows={12}
+            placeholder="Write the next plot (500–10,000 characters)"
+            className="border-border bg-surface text-foreground placeholder:text-muted w-full resize-y rounded border px-3 py-2 text-sm leading-relaxed focus:border-accent focus:outline-none disabled:opacity-50"
+          />
+          <div className="mt-1 text-xs">
+            <span
+              className={
+                content.length > 0 && !valid ? "text-error" : "text-muted"
+              }
+            >
+              {charCount.toLocaleString()} /{" "}
+              {MIN_CONTENT_LENGTH.toLocaleString()}–
+              {MAX_CONTENT_LENGTH.toLocaleString()} chars
+            </span>
+          </div>
+        </div>
+
+        {/* Status */}
+        {state === "error" && (
+          <div className="border-error/30 text-error rounded border px-3 py-2 text-xs">
+            {error}
+          </div>
+        )}
+        {busy && (
+          <div className="border-border text-muted rounded border px-3 py-2 text-xs">
+            {STATE_LABELS[state]}
+          </div>
+        )}
+
+        {/* Submit */}
+        <button
+          type="submit"
+          disabled={!canSubmit || busy}
+          className="border-accent text-accent hover:bg-accent hover:text-background w-full rounded border py-2.5 text-sm font-medium transition-colors disabled:opacity-50"
+        >
+          {busy ? STATE_LABELS[state] : "Chain Plot"}
+        </button>
+      </form>
+    </div>
+  );
+}
diff --git a/src/app/create/page.tsx b/src/app/create/page.tsx
index 67ae38a2..c9dbf907 100644
--- a/src/app/create/page.tsx
+++ b/src/app/create/page.tsx
@@ -8,7 +8,9 @@ import {
   MIN_CONTENT_LENGTH,
   MAX_CONTENT_LENGTH,
 } from "../../../lib/content";
-import { usePublishStoryline, type PublishState } from "../../hooks/usePublish";
+import { usePublish, type PublishState } from "../../hooks/usePublish";
+import { storyFactoryAbi } from "../../../lib/contracts/abi";
+import { STORY_FACTORY } from "../../../lib/contracts/constants";
 import Link from "next/link";
 
 const STATE_LABELS: Record<PublishState, string> = {
@@ -27,7 +29,7 @@ export default function CreateStorylinePage() {
   const [content, setContent] = useState("");
   const [hasDeadline, setHasDeadline] = useState(false);
 
-  const { state, error, publish, reset } = usePublishStoryline();
+  const { state, error, execute, reset } = usePublish();
   const { valid, charCount } = validateContentLength(content);
   const titleValid = title.trim().length > 0;
   const canSubmit =
@@ -79,7 +81,18 @@ export default function CreateStorylinePage() {
       <form
         onSubmit={(e) => {
           e.preventDefault();
-          if (canSubmit) publish(title.trim(), content, hasDeadline);
+          if (canSubmit)
+            execute({
+              content,
+              uploadKeyPrefix: "plotlink/genesis",
+              indexerRoute: "/api/index/storyline",
+              buildWriteCall: (cid, contentHash) => ({
+                address: STORY_FACTORY,
+                abi: storyFactoryAbi as unknown as [],
+                functionName: "createStoryline",
+                args: [title.trim(), cid, contentHash, hasDeadline],
+              }),
+            });
         }}
         className="mt-8 space-y-6"
       >
diff --git a/src/hooks/useChainPlot.ts b/src/hooks/useChainPlot.ts
new file mode 100644
index 00000000..9b350fd4
--- /dev/null
+++ b/src/hooks/useChainPlot.ts
@@ -0,0 +1,33 @@
+"use client";
+
+import { useCallback } from "react";
+import { usePublish } from "./usePublish";
+import { storyFactoryAbi } from "../../lib/contracts/abi";
+import { STORY_FACTORY } from "../../lib/contracts/constants";
+
+/**
+ * Chain a plot to an existing storyline (P3-3).
+ * Reuses the shared publishing state machine from usePublish.
+ */
+export function useChainPlot() {
+  const { state, error, txHash, execute, reset } = usePublish();
+
+  const chainPlot = useCallback(
+    async (storylineId: number, content: string) => {
+      await execute({
+        content,
+        uploadKeyPrefix: `plotlink/plots/${storylineId}`,
+        indexerRoute: "/api/index/plot",
+        buildWriteCall: (cid, contentHash) => ({
+          address: STORY_FACTORY,
+          abi: storyFactoryAbi as unknown as [],
+          functionName: "chainPlot",
+          args: [BigInt(storylineId), cid, contentHash],
+        }),
+      });
+    },
+    [execute],
+  );
+
+  return { state, error, txHash, chainPlot, reset };
+}
diff --git a/src/hooks/usePublish.ts b/src/hooks/usePublish.ts
index 68402e0f..003dea2c 100644
--- a/src/hooks/usePublish.ts
+++ b/src/hooks/usePublish.ts
@@ -2,11 +2,9 @@
 
 import { useState, useCallback, useRef } from "react";
 import { useWriteContract } from "wagmi";
-import { storyFactoryAbi } from "../../lib/contracts/abi";
-import { STORY_FACTORY } from "../../lib/contracts/constants";
 import { hashContent } from "../../lib/content";
 import { publicClient } from "../../lib/rpc";
-import type { Hex } from "viem";
+import type { Hex, Abi } from "viem";
 
 export type PublishState =
   | "idle"
@@ -17,30 +15,39 @@ export type PublishState =
   | "published"
   | "error";
 
-interface PublishResult {
-  state: PublishState;
-  error: string | null;
-  txHash: Hex | undefined;
-  publish: (
-    title: string,
-    content: string,
-    hasDeadline: boolean,
-  ) => Promise<void>;
-  reset: () => void;
+interface WriteCall {
+  address: `0x${string}`;
+  abi: Abi;
+  functionName: string;
+  args: readonly unknown[];
 }
 
-export function usePublishStoryline(): PublishResult {
+interface PublishOptions {
+  content: string;
+  uploadKeyPrefix: string;
+  indexerRoute: string;
+  buildWriteCall: (cid: string, contentHash: Hex) => WriteCall;
+}
+
+/**
+ * Shared publishing state machine for StoryFactory write flows.
+ *
+ * Manages the 5-state flow: uploading -> confirming -> pending -> indexing -> published.
+ * Caches CID keyed by content hash for retry (skips re-upload if content unchanged).
+ */
+export function usePublish() {
   const [state, setState] = useState<PublishState>("idle");
   const [error, setError] = useState<string | null>(null);
+  const [txHash, setTxHash] = useState<Hex | undefined>(undefined);
   const cachedCid = useRef<{ cid: string; contentHash: string } | null>(null);
 
-  const { writeContractAsync, data: txHash } = useWriteContract();
+  const { writeContractAsync } = useWriteContract();
 
-  const publish = useCallback(
-    async (title: string, content: string, hasDeadline: boolean) => {
+  const execute = useCallback(
+    async (opts: PublishOptions) => {
       try {
         setError(null);
-        const contentHash = hashContent(content);
+        const contentHash = hashContent(opts.content);
 
         // 1. Upload to IPFS (reuse cached CID only if content unchanged)
         let cid: string;
@@ -55,8 +62,8 @@ export function usePublishStoryline(): PublishResult {
             method: "POST",
             headers: { "Content-Type": "application/json" },
             body: JSON.stringify({
-              content,
-              key: `plotlink/genesis/${Date.now()}.txt`,
+              content: opts.content,
+              key: `${opts.uploadKeyPrefix}/${Date.now()}.txt`,
             }),
           });
           if (!res.ok) throw new Error("IPFS upload failed");
@@ -67,24 +74,21 @@ export function usePublishStoryline(): PublishResult {
 
         // 2. Submit tx to wallet
         setState("confirming");
+        const writeCall = opts.buildWriteCall(cid, contentHash);
 
-        const hash = await writeContractAsync({
-          address: STORY_FACTORY,
-          abi: storyFactoryAbi,
-          functionName: "createStoryline",
-          args: [title, cid, contentHash, hasDeadline],
-        });
+        const hash = await writeContractAsync(writeCall);
+        setTxHash(hash);
 
-        // 3. Wait for tx confirmation via viem publicClient
+        // 3. Wait for tx confirmation
         setState("pending");
         await publicClient.waitForTransactionReceipt({ hash });
 
         // 4. Trigger indexer
         setState("indexing");
-        await fetch("/api/index/storyline", {
+        await fetch(opts.indexerRoute, {
           method: "POST",
           headers: { "Content-Type": "application/json" },
-          body: JSON.stringify({ txHash: hash, content }),
+          body: JSON.stringify({ txHash: hash, content: opts.content }),
         });
 
         // 5. Done
@@ -103,8 +107,9 @@ export function usePublishStoryline(): PublishResult {
   const reset = useCallback(() => {
     setState("idle");
     setError(null);
+    setTxHash(undefined);
     cachedCid.current = null;
   }, []);
 
-  return { state, error, txHash, publish, reset };
+  return { state, error, txHash, execute, reset };
 }