diff --git a/libs/shared-state-books/src/lib/books.reducer.ts b/libs/shared-state-books/src/lib/books.reducer.ts
index f609a26..b653d33 100644
--- a/libs/shared-state-books/src/lib/books.reducer.ts
+++ b/libs/shared-state-books/src/lib/books.reducer.ts
@@ -10,3 +10,29 @@ const updateBook = (books: BookModel[], changes: BookModel) =>
   });
 const deleteBook = (books: BookModel[], bookId: string) =>
   books.filter((book) => bookId !== book.id);
+
+export interface State {
+  collection: BookModel[];
+  activeBookId: string | null;
+}
+
+export const initialState: State = {
+  collection: [],
+  activeBookId: null,
+};
+
+export const reducer = createReducer(
+  initialState,
+  on(BooksPageActions.clearSelectedBook, BooksPageActions.enter, (state) => {
+    return {
+      ...state,
+      activeBookId: null,
+    };
+  }),
+  on(BooksPageActions.selectBook, (state, action) => {
+    return {
+      ...state,
+      activeBookId: action.bookId,
+    };
+  })
+);