Update to Drupal 8.0.0 beta 14. For more information, see https://drupal.org/node/2544542

core/modules/book/migration_templates/d6_book.yml

@@ -0,0 +1,23 @@
+id: d6_book
+label: Drupal 6 books
+migration_tags:
+  - Drupal 6
+source:
+  plugin: d6_book
+process:
+  nid: nid
+  'book/bid': bid
+  'book/weight': weight
+  'book/pid':
+    -
+      plugin: skip_on_empty
+      method: process
+      source: plid
+    -
+      plugin: migration
+      migration: d6_book
+destination:
+  plugin: book
+migration_dependencies:
+  required:
+    - d6_node

core/modules/book/migration_templates/d6_book_settings.yml

@@ -0,0 +1,17 @@
+id: d6_book_settings
+label: Drupal 6 book configuration
+migration_tags:
+  - Drupal 6
+source:
+  plugin: variable
+  variables:
+    - book_child_type
+    - book_block_mode
+    - book_allowed_types
+process:
+  child_type: book_child_type
+  'block/navigation/mode': book_block_mode
+  allowed_types: book_allowed_types
+destination:
+  plugin: config
+  config_name: book.settings