diff --git a/src/App.tsx b/src/App.tsx
index 3c91ae6..f982dbf 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -5,6 +5,7 @@ import { AuthProvider, useAuth } from './auth/AuthContext'
 import { LoginForm } from './auth/LoginForm'
 import { RequireAuth } from './auth/RequireAuth'
 import { BookList } from './books/BookList'
+import { BookDetail } from './books/BookDetail'
 import { secondaryButton } from './ui'
 
 export function App() {
@@ -24,6 +25,7 @@ export function AppRoutes() {
       <Route element={<RequireAuth />}>
         <Route element={<Shell />}>
           <Route path="/books" element={<BookList />} />
+          <Route path="/books/:id" element={<BookDetail />} />
         </Route>
       </Route>
       <Route path="*" element={<Navigate to="/books" replace />} />
diff --git a/src/books/BookDetail.test.tsx b/src/books/BookDetail.test.tsx
new file mode 100644
index 0000000..a4c63db
--- /dev/null
+++ b/src/books/BookDetail.test.tsx
@@ -0,0 +1,72 @@
+import { screen, waitFor } from '@testing-library/react'
+import { describe, expect, it } from 'vitest'
+import type { Book } from '../api'
+import { dune, renderApp, signedIn } from '../test/helpers'
+
+function withProgress(current_page: number): Book {
+  const status = current_page === 0 ? 'not_started' : current_page === dune.total_pages ? 'finished' : 'reading'
+  return { ...dune, current_page, status }
+}
+
+describe('BookDetail', () => {
+  it('updates progress and reflects it in the bar', async () => {
+    const calls = signedIn({
+      'GET /api/books/7': () => [200, dune],
+      'PATCH /api/books/7': ({ body }) => [200, withProgress((body as { current_page: number }).current_page)],
+    })
+    const user = renderApp('/books/7')
+    expect(await screen.findByText('142 / 380 (37%)')).toBeInTheDocument()
+
+    const input = screen.getByLabelText('Current page')
+    await user.clear(input)
+    await user.type(input, '200')
+    await user.click(screen.getByRole('button', { name: 'Save progress' }))
+
+    expect(await screen.findByText('200 / 380 (53%)')).toBeInTheDocument()
+    expect(calls).toContainEqual({ method: 'PATCH', path: '/api/books/7', body: { current_page: 200 } })
+  })
+
+  it('marks a book finished', async () => {
+    signedIn({
+      'GET /api/books/7': () => [200, dune],
+      'PATCH /api/books/7': () => [200, withProgress(380)],
+    })
+    const user = renderApp('/books/7')
+    await user.click(await screen.findByRole('button', { name: 'Mark finished' }))
+    expect(await screen.findByText('380 / 380 (100%)')).toBeInTheDocument()
+    expect(screen.getByText('Finished')).toBeInTheDocument()
+  })
+
+  it('shows the server message when a progress update is rejected', async () => {
+    signedIn({
+      'GET /api/books/7': () => [200, dune],
+      'PATCH /api/books/7': () => [400, { error: 'current_page must be between 0 and 100000', field: 'current_page' }],
+    })
+    const user = renderApp('/books/7')
+    await user.click(await screen.findByRole('button', { name: 'Save progress' }))
+    // findByText, not findByRole('alert'): once Task 11 mounts the journal, the page may show more than one alert.
+    expect(await screen.findByText('current_page must be between 0 and 100000')).toHaveAttribute('role', 'alert')
+    expect(screen.getByLabelText('Current page')).toHaveAttribute('aria-invalid', 'true')
+  })
+
+  it('shows not found for a missing or foreign book', async () => {
+    signedIn({ 'GET /api/books/999': () => [404, { error: 'Book not found' }] })
+    renderApp('/books/999')
+    expect(await screen.findByRole('heading', { name: 'Book not found' })).toBeInTheDocument()
+    expect(screen.getByRole('link', { name: /back to library/i })).toHaveAttribute('href', '/books')
+  })
+
+  it('deletes after confirmation and returns to the list', async () => {
+    const calls = signedIn({
+      'GET /api/books/7': () => [200, dune],
+      'DELETE /api/books/7': () => [204],
+      'GET /api/books': () => [200, []],
+    })
+    const user = renderApp('/books/7')
+    await user.click(await screen.findByRole('button', { name: 'Delete book' }))
+    expect(screen.getByRole('dialog')).toHaveTextContent('Delete “Dune”?')
+    await user.click(screen.getByRole('button', { name: 'Yes, delete' }))
+    expect(await screen.findByText('No books yet. Add your first one.')).toBeInTheDocument()
+    await waitFor(() => expect(calls.some((c) => c.method === 'DELETE' && c.path === '/api/books/7')).toBe(true))
+  })
+})
diff --git a/src/books/BookDetail.tsx b/src/books/BookDetail.tsx
new file mode 100644
index 0000000..8875c2a
--- /dev/null
+++ b/src/books/BookDetail.tsx
@@ -0,0 +1,160 @@
+import { useEffect, useState, type FormEvent } from 'react'
+import { Link, useNavigate, useParams } from 'react-router'
+import { api, ApiError, errorMessage, type Book } from '../api'
+import { card, dangerButton, inputClass, labelText, primaryButton, secondaryButton } from '../ui'
+import { ProgressBar, StatusBadge } from './Progress'
+
+export function BookDetail() {
+  const { id } = useParams()
+  const navigate = useNavigate()
+  const [book, setBook] = useState<Book | null>(null)
+  const [loadError, setLoadError] = useState<{ notFound: boolean; message: string } | null>(null)
+  const [attempt, setAttempt] = useState(0)
+  const [page, setPage] = useState('')
+  const [progressError, setProgressError] = useState<string | null>(null)
+  const [confirmingDelete, setConfirmingDelete] = useState(false)
+  const [deleteError, setDeleteError] = useState<string | null>(null)
+
+  useEffect(() => {
+    let cancelled = false
+    setLoadError(null)
+    api<Book>('GET', `/books/${id}`).then(
+      (found) => {
+        if (cancelled) return
+        setBook(found)
+        setPage(String(found.current_page))
+      },
+      (err) => {
+        if (!cancelled) setLoadError({ notFound: err instanceof ApiError && err.status === 404, message: errorMessage(err) })
+      },
+    )
+    return () => {
+      cancelled = true
+    }
+  }, [id, attempt])
+
+  if (loadError?.notFound) {
+    return (
+      <div className={card}>
+        <h1 className="text-xl font-semibold">Book not found</h1>
+        <Link to="/books" className="mt-2 inline-block text-indigo-700 underline">
+          ← Back to library
+        </Link>
+      </div>
+    )
+  }
+  if (loadError) {
+    return (
+      <div role="alert" className="flex items-center gap-3 text-red-700">
+        <span>{loadError.message}</span>
+        <button type="button" className={secondaryButton} onClick={() => setAttempt((n) => n + 1)}>
+          Retry
+        </button>
+      </div>
+    )
+  }
+  if (!book) return <p className="text-slate-500">Loading…</p>
+  const current = book
+
+  async function saveProgress(currentPage: number) {
+    setProgressError(null)
+    try {
+      const updated = await api<Book>('PATCH', `/books/${current.id}`, { current_page: currentPage })
+      setBook(updated)
+      setPage(String(updated.current_page))
+    } catch (err) {
+      setProgressError(errorMessage(err))
+    }
+  }
+
+  async function deleteBook() {
+    setDeleteError(null)
+    try {
+      await api('DELETE', `/books/${current.id}`)
+      navigate('/books', { replace: true })
+    } catch (err) {
+      setDeleteError(errorMessage(err))
+    }
+  }
+
+  function submitProgress(event: FormEvent) {
+    event.preventDefault()
+    void saveProgress(Number(page))
+  }
+
+  return (
+    <article className="space-y-6">
+      <Link to="/books" className="text-sm text-indigo-700 underline">
+        ← Back to library
+      </Link>
+      <header className={card}>
+        <div className="flex items-start justify-between gap-3">
+          <div>
+            <h1 className="text-2xl font-semibold">{book.title}</h1>
+            <p className="text-slate-600">{`${book.author} · ${book.genre.name}`}</p>
+          </div>
+          <StatusBadge status={book.status} />
+        </div>
+        <ProgressBar book={book} />
+        <form onSubmit={submitProgress} className="mt-4 flex flex-wrap items-end gap-2">
+          <label>
+            <span className={labelText}>Current page</span>
+            <input
+              type="number"
+              className={`${inputClass} w-32`}
+              min={0}
+              max={book.total_pages}
+              value={page}
+              onChange={(e) => setPage(e.target.value)}
+              required
+              aria-invalid={progressError ? true : undefined}
+              aria-describedby={progressError ? 'progress-error' : undefined}
+            />
+          </label>
+          <button type="submit" className={primaryButton}>
+            Save progress
+          </button>
+          <button
+            type="button"
+            className={secondaryButton}
+            disabled={book.current_page === book.total_pages}
+            onClick={() => void saveProgress(book.total_pages)}
+          >
+            Mark finished
+          </button>
+        </form>
+        {progressError && (
+          <p id="progress-error" role="alert" className="mt-2 text-sm text-red-700">
+            {progressError}
+          </p>
+        )}
+        <div className="mt-4 flex gap-2">
+          <Link to={`/books/${book.id}/edit`} className={secondaryButton}>
+            Edit
+          </Link>
+          <button type="button" className={dangerButton} onClick={() => setConfirmingDelete(true)}>
+            Delete book
+          </button>
+        </div>
+        {confirmingDelete && (
+          <dialog open aria-labelledby="delete-prompt" className={`relative mt-4 ${card} ring-2 ring-red-200`}>
+            <p id="delete-prompt">{`Delete “${book.title}”? This also deletes its reading journal.`}</p>
+            <div className="mt-3 flex gap-2">
+              <button type="button" className={dangerButton} onClick={() => void deleteBook()}>
+                Yes, delete
+              </button>
+              <button type="button" className={secondaryButton} onClick={() => setConfirmingDelete(false)}>
+                Cancel
+              </button>
+            </div>
+            {deleteError && (
+              <p role="alert" className="mt-2 text-sm text-red-700">
+                {deleteError}
+              </p>
+            )}
+          </dialog>
+        )}
+      </header>
+    </article>
+  )
+}