diff --git a/localgov_subsites_extras.api.php b/localgov_subsites_extras.api.php
new file mode 100644
index 0000000..ebb7f5c
--- /dev/null
+++ b/localgov_subsites_extras.api.php
@@ -0,0 +1,44 @@
+<?php
+
+/**
+ * @file
+ * Hooks provided by the Locagov Subsites Extras module.
+ */
+
+use Drupal\node\NodeInterface;
+
+/**
+ * @addtogroup hooks
+ * @{
+ */
+
+/**
+ * Alter the current node, before subsite determination.
+ *
+ * This alter hook is called before we walk the menu tree to determine if we're
+ * looking at a page in a subsite or not.
+ *
+ * It'll be passed the current node, acquired from routeMatch. If no node is
+ * found there, this hook will be passed null. This gives the opportunity to
+ * include non-node pages in a subsite if you wish.
+ *
+ * If you want to indicate that a subsite is not being viewed, set $node to
+ * NULL.
+ *
+ * Usually, this hook will be used to use a property of the node passed, such as
+ * a reference to another node (such as the parent node field for guides,
+ * directories, etc) to swop out the current node for a different node, which is
+ * in the menu and therefore part of a subsite.
+ */
+function hook_localgov_subsites_extras_current_node_alter(?NodeInterface &$node) {
+  if ($node instanceof NodeInterface && $node->hasField('field_parent')) {
+    $parent = $node->field_parent->entity;
+    if ($parent instanceof NodeInterface) {
+      $node = $parent;
+    }
+  }
+}
+
+/**
+ * @} End of "addtogroup hooks".
+ */
diff --git a/localgov_subsites_extras.module b/localgov_subsites_extras.module
index c869f7b..8444d0c 100644
--- a/localgov_subsites_extras.module
+++ b/localgov_subsites_extras.module
@@ -7,6 +7,8 @@
 
 declare(strict_types=1);
 
+include 'localgov_subsites_extras_hooks.inc';
+
 /**
  * Implements hook_preprocess_node().
  *
@@ -69,5 +71,4 @@ function localgov_subsites_extras_entity_bundle_create($entity_type_id, $bundle)
     $type->setThirdPartySetting('menu_ui', 'available_menus', $availableMenus);
     $type->save();
   }
-
 }
diff --git a/localgov_subsites_extras.services.yml b/localgov_subsites_extras.services.yml
index b245fe7..687c9ca 100644
--- a/localgov_subsites_extras.services.yml
+++ b/localgov_subsites_extras.services.yml
@@ -1,7 +1,7 @@
 services:
   localgov_subsites_extras.service:
     class: Drupal\localgov_subsites_extras\Service\SubsiteService
-    arguments: ['@entity_type.manager', '@plugin.manager.menu.link', '@current_route_match', '@config.factory']
+    arguments: ['@config.factory', '@entity_type.manager', '@plugin.manager.menu.link', '@module_handler', '@current_route_match']
   cache_context.subsites:
     class: Drupal\localgov_subsites_extras\Cache\SubsitesCacheContext
     arguments:
diff --git a/localgov_subsites_extras_hooks.inc b/localgov_subsites_extras_hooks.inc
new file mode 100644
index 0000000..7456684
--- /dev/null
+++ b/localgov_subsites_extras_hooks.inc
@@ -0,0 +1,45 @@
+<?php
+
+/**
+ * @file
+ * Hooks that we're temporarily implementing on behalf of other modules.
+ *
+ * Ideally, we want these hook implementations in their respective modules. For
+ * the moment, we've implemented them here, and when this module is heading
+ * towards a proper release, we'll open PRs to move them. Each hook is wrapped
+ * in function_exists, so that the hook can exist in both modules temporarily.
+ */
+
+use Drupal\node\NodeInterface;
+
+if (!function_exists('localgov_directories_localgov_subsites_extras_current_node_alter')) {
+
+  /**
+   * Implements hook_localgov_subsites_extras_current_node_alter().
+   */
+  function localgov_directories_localgov_subsites_extras_current_node_alter(?NodeInterface &$node) {
+    if ($node instanceof NodeInterface && $node->hasField('localgov_directory_channels')) {
+      $directoryChannel = $node->localgov_directory_channels->entity;
+      if ($directoryChannel instanceof NodeInterface) {
+        $node = $directoryChannel;
+      }
+    }
+  }
+
+}
+
+if (!function_exists('localgov_guides_localgov_subsites_extras_current_node_alter')) {
+
+  /**
+   * Implements hook_localgov_subsites_extras_current_node_alter().
+   */
+  function localgov_guides_localgov_subsites_extras_current_node_alter(?NodeInterface &$node) {
+    if ($node instanceof NodeInterface && $node->hasField('localgov_guides_parent')) {
+      $guideParent = $node->localgov_guides_parent->entity;
+      if ($guideParent instanceof NodeInterface) {
+        $node = $guideParent;
+      }
+    }
+  }
+
+}
diff --git a/src/Service/SubsiteService.php b/src/Service/SubsiteService.php
index 63ccd71..f277817 100644
--- a/src/Service/SubsiteService.php
+++ b/src/Service/SubsiteService.php
@@ -6,6 +6,7 @@
 
 use Drupal\Core\Config\ConfigFactory;
 use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Extension\ModuleHandlerInterface;
 use Drupal\Core\Menu\MenuLinkManagerInterface;
 use Drupal\Core\Routing\RouteMatchInterface;
 use Drupal\node\NodeInterface;
@@ -15,30 +16,34 @@
  */
 class SubsiteService implements SubsiteServiceInterface {
 
-  // Disable phpcs for a bit, so we don't have to add a load of stuff that's
-  // made redundant by type hints.
-  // phpcs:disable
-  private EntityTypeManagerInterface $entityTypeManager;
-  private MenuLinkManagerInterface $menuLinkService;
-  private RouteMatchInterface $routeMatch;
-  private ConfigFactory $configFactory;
+  /**
+   * Subsite homepage.
+   *
+   * @var \Drupal\node\NodeInterface|null
+   */
   private ?NodeInterface $subsiteHomePage;
-  private bool $searched = false;
+
+  /**
+   * Searched flag.
+   *
+   * @var bool
+   */
+  private bool $searched = FALSE;
+
+  /**
+   * Subsite content types.
+   *
+   * @var array|null
+   */
   private ?array $subsiteTypes = [];
-  private ?string $themeField;
 
   public function __construct(
-    EntityTypeManagerInterface $entityTypeManager,
-    MenuLinkManagerInterface $menuLinkService,
-    RouteMatchInterface $routeMatch,
-    ConfigFactory $configFactory
-  ) {
-    $this->entityTypeManager = $entityTypeManager;
-    $this->menuLinkService = $menuLinkService;
-    $this->routeMatch = $routeMatch;
-    $this->configFactory = $configFactory;
-  }
-  // phpcs:enable
+    private ConfigFactory $configFactory,
+    private EntityTypeManagerInterface $entityTypeManager,
+    private MenuLinkManagerInterface $menuLinkService,
+    private ModuleHandlerInterface $moduleHandler,
+    private RouteMatchInterface $routeMatch,
+  ) {}
 
   /**
    * {@inheritDoc}
@@ -58,13 +63,13 @@ public function getHomePage(): ?NodeInterface {
    */
   public function getCurrentSubsiteTheme(): ?string {
 
-    $this->themeField = $this->configFactory->get('localgov_subsites_extras.settings')->get('theme_field');
+    $themeField = $this->configFactory->get('localgov_subsites_extras.settings')->get('theme_field');
 
     // If the current node is part of a subsite, $subsiteHomePage will be the
     // subsite's homepage node. If it's not, it'll be null.
     $subsiteHomePage = $this->getHomePage();
     if ($subsiteHomePage) {
-      return $subsiteHomePage->get($this->themeField)->value;
+      return $subsiteHomePage->get($themeField)->value;
     }
 
     return NULL;
@@ -80,7 +85,7 @@ private function isSubsiteType(NodeInterface $node): bool {
   /**
    * Walks up the menu tree to look for a subsite homepage node.
    */
-  private function walkMenuTree(NodeInterface $node) {
+  private function walkMenuTree(NodeInterface $node): ?NodeInterface {
 
     if ($this->isSubsiteType($node)) {
       return $node;
@@ -91,10 +96,9 @@ private function walkMenuTree(NodeInterface $node) {
     if (!empty($result)) {
       $menuLink = reset($result);
       $parentMenuLinkID = $menuLink->getParent();
-
       if ($parentMenuLinkID) {
         $parentNode = $this->loadNodeForMenuLink($parentMenuLinkID);
-        return $this->walkMenuTree($parentNode);
+        return $parentNode ? $this->walkMenuTree($parentNode) : NULL;
       }
     }
     return NULL;
@@ -103,7 +107,7 @@ private function walkMenuTree(NodeInterface $node) {
   /**
    * Loads the node for the supplied menu link ID.
    */
-  private function loadNodeForMenuLink($menuLinkContentID) {
+  private function loadNodeForMenuLink($menuLinkContentID): ?NodeInterface {
     $menuLink = $this->menuLinkService->createInstance($menuLinkContentID);
     $pluginDefinition = $menuLink->getPluginDefinition();
 
@@ -135,6 +139,8 @@ private function findHomePage(?NodeInterface $node = NULL): ?NodeInterface {
       }
     }
 
+    $this->moduleHandler->alter('localgov_subsites_extras_current_node', $node);
+
     if (!$node instanceof NodeInterface) {
       return NULL;
     }
@@ -144,16 +150,7 @@ private function findHomePage(?NodeInterface $node = NULL): ?NodeInterface {
       $this->subsiteTypes = $subsiteTypes;
     }
 
-    $subsiteHomePage = $this->walkMenuTree($node);
-
-    // @todo Move this out to an event or hook or something.
-    if (empty($subsiteHomePage) && $node->getType() === 'localgov_directories_page') {
-      /** @var \Drupal\node\NodeInterface $directoryChannel */
-      $directoryChannel = $node->localgov_directory_channels->entity;
-      $subsiteHomePage = $this->walkMenuTree($directoryChannel);
-    }
-
-    return $subsiteHomePage;
+    return $this->walkMenuTree($node);
   }
 
 }
diff --git a/tests/src/Functional/SubsiteTest.php b/tests/src/Functional/SubsiteTest.php
index 215d5d4..52668cb 100644
--- a/tests/src/Functional/SubsiteTest.php
+++ b/tests/src/Functional/SubsiteTest.php
@@ -3,7 +3,6 @@
 namespace Drupal\Tests\localgov_subsites_extras\Functional;
 
 use Drupal\menu_link_content\Entity\MenuLinkContent;
-use Drupal\node\Entity\Node;
 use Drupal\Tests\BrowserTestBase;
 
 /**
@@ -22,49 +21,77 @@ class SubsiteTest extends BrowserTestBase {
   protected static $modules = [
     'localgov_subsites',
     'localgov_subsites_extras',
+    'localgov_guides',
   ];
 
   /**
-   * Test that we can set up a subsite using this module.
+   * Creates a menu link to the given node in the subsites menu.
    */
-  public function testLoadAdminView() {
+  protected function createMenuLinkForNode($node, $parentLink = NULL) {
+    $properties = [
+      'link' => [['uri' => 'entity:node/' . $node->id()]],
+      'title' => $node->label(),
+      'menu_name' => 'subsites',
+    ];
+    if ($parentLink instanceof MenuLinkContent) {
+      $properties['parent'] = 'menu_link_content:' . $parentLink->uuid();
+    }
+    $menuLink = MenuLinkContent::create($properties);
+    $menuLink->save();
+    return $menuLink;
+  }
 
-    $user = $this->createUser([], 'admintestuser', TRUE);
+  /**
+   * Test that we can set up a subsite using this module.
+   *
+   * Structure is a single subsite page under a subsite overview.
+   */
+  public function testSubsitePage() {
 
-    // "theme_a" is the only default value in a fresh install of
-    // localgov_subsites.
-    $parentNode = Node::create([
+    // "theme_a" is the only value in a fresh install of localgov_subsites.
+    $parentNode = $this->createNode([
       'type' => 'localgov_subsites_overview',
-      'title' => $this->randomMachineName(),
-      'uid' => $user->id(),
-      'status' => 1,
       'localgov_subsites_theme' => 'theme_a',
     ]);
-    $parentNode->save();
+    $parentMenuLink = $this->createMenuLinkForNode($parentNode);
 
-    $parentMenuLink = MenuLinkContent::create([
-      'link' => [['uri' => 'entity:node/' . $parentNode->id()]],
-      'title' => $parentNode->label(),
-      'menu_name' => 'subsites',
+    $childNode = $this->createNode([
+      'type' => 'localgov_subsites_page',
     ]);
-    $parentMenuLink->save();
+    $this->createMenuLinkForNode($childNode, $parentMenuLink);
 
-    $childNode = Node::create([
-      'type' => 'localgov_subsites_page',
-      'title' => $this->randomMachineName(),
-      'uid' => $user->id(),
-      'status' => 1,
+    $this->drupalGet('/node/' . $childNode->id());
+
+    // Check the class for the color scheme is on the body of the child node.
+    $this->assertSession()->elementAttributeContains('xpath', '/body', 'class', 'subsite-extra--color-theme_a');
+  }
+
+  /**
+   * Test that we can set up a guide in a subsite using this module.
+   *
+   * Structure is a single guide page under a guide overview under a subsite
+   * overview.
+   */
+  public function testGuidePage() {
+
+    // "theme_a" is the only value in a fresh install of localgov_subsites.
+    $subsiteNode = $this->createNode([
+      'type' => 'localgov_subsites_overview',
+      'localgov_subsites_theme' => 'theme_a',
     ]);
-    $childNode->save();
+    $subsiteMenuLink = $this->createMenuLinkForNode($subsiteNode);
 
-    MenuLinkContent::create([
-      'link' => [['uri' => 'entity:node/' . $childNode->id()]],
-      'title' => $childNode->label(),
-      'menu_name' => 'subsites',
-      'parent' => 'menu_link_content:' . $parentMenuLink->uuid(),
-    ])->save();
+    $guideOverviewNode = $this->createNode([
+      'type' => 'localgov_guides_overview',
+    ]);
+    $this->createMenuLinkForNode($guideOverviewNode, $subsiteMenuLink);
 
-    $this->drupalGet('/node/' . $childNode->id());
+    $guidePageNode = $this->createNode([
+      'type' => 'localgov_guides_page',
+      'localgov_guides_parent' => $guideOverviewNode->id(),
+    ]);
+
+    $this->drupalGet('/node/' . $guidePageNode->id());
 
     // Check the class for the color scheme is on the body of the child node.
     $this->assertSession()->elementAttributeContains('xpath', '/body', 'class', 'subsite-extra--color-theme_a');