Castle Chase

This ending is the grand daddy of all endings! Not only is it the most complex ending in the game, it also gave Racheal a headache or twelve programming it. Get ready to follow along, I'm not surprised you needed help for this one! Even step one if different from all the rest.
The hint babe linked to this ending is Haily.

1. After the opening conversation with Madam Appleby, go to Caden's room in the children's wing and get the "Noisemaker." You won't need it for a while, but you're here so you might as well grab it.
   NOTE: Using the "Noisemaker" in random places makes a fun sound.
2. Now, head to the kitchen and talk to Gilroy.
3. Pick "Did you want some help?" to help Gilroy make lunch for the guests. At the end of the conversation, he will give you the "Sandwich" he made. Yum...!
4. While in the kitchen, grab the "Red Herring" and then head up to the wine cellar to get the "Lantern". You will need them both later.
5. Find and talk to Gilroy outside of your Father's room. Monica will offer to help him with the laundry and Gilroy will now be following you.
   NOTE: When a boy is following you, you are unable to use any item except your Diary to save.
6. Take Gilroy to the laundry room in the servant's quarters in order to trigger the cutscene. Pick "I'll take one of these when he's not looking." during the conversation to take one of the uniforms, or pick it up off the table after the scene. Either way, you need the "Servant Clothes."
7. Head downstairs and towards the library. Skyler will be blocking the entrance. Talk to him once and then give him the "Sandwich" in order to make him move.
8. Go into the library and talk to Clair.
9. Now, head outside through the courtyard to the training grounds. A cutscene will trigger where you'll be asked to help Erol get past a monster. Erol will now be following you.
10. Head into the squire's dorms to trigger another cutscene.
11. Give the "Red Herring" to the cat and you will acquire the "Antique Chain" and "Kitty" items.
12. Once you leave the squire's dorms you will be confronted by Aydin who will ask you to give him the "Antique Chain." You can give the chain back to him, or give it to Clair in the library. Either way will move Clair from his current position.
13. If you did not give the "Antique Chain" to Aydin, give it to Clair now in the library.
14. Search the bookcase behind where Clair was standing before to reveal a secret passage that takes you to the catacombs.
15. Use the "Lantern" so that you can see where you are going.
16. Make your way past the traps until you come to a person trapped under a net. Examine the person, Hyde, and pick "Let me help you." He'll be ungrateful about it, but the conversation will continue. Pick "I'll help you!"
17. Give Hyde the "Servant Clothes" and he will follow you. Take him to the servants’ quarters and store him in the boys' room for now. Hyde will give you the "Castle Plans."
    NOTE: If you step on a net while Hyde is with you, there is no penalty. Asides from shame.
18. The following step is completely optional and works only as a hint. Head to the entrance and grab the "Strange Drawing" from the coat room. Now procede back to Skyler's room and show him the "Strange Drawing" so that way he'll lighten up a bit. Next, show him the "Castle Plans" and he will tell you that there are two keys that need to be used on the throne to open the way to the treasure room. The keys are kept with two people who the King trusts; Master Reva and Sir Conrad are these two people.
19. Head to the entrance and use the "Noisemaker" on Reva to scare her. She'll drop something, pick it up and you'll get "One Throne Key."
20. With one key in tow, you must now go get the second one from Sir Conrad. This key can be a bit tricky to get, but there are two ways of doing it. The shortest way is using the cat. Use the "Kitty" on the one tile where Conrad can see the cat and not you. Once he starts to move, quickly dodge to the side and into on the the dorm rooms. Conrad will follow the kitten right out of the building and you can search his dresser for the key giving you a "Pair of Throne Keys." Be sure to pick the "Kitty" back up once you leave the dorms. You'll need him again later.
    NOTE: You can also get the second key by advancing Aydin to Step 13. Once he's reached this step you can enter the squires' dorms and a scene between Aydin and Conrad will occur where Aydin leads Conrad out of the dorms. Search his dresser during this time to get the "Pair of Throne Keys." Once you leave the dorms, Conrad will return and this scene will not trigger again. Also, after triggering the conversation between Skyler and Aydin in Skyler's room (Step 19) this scene can no longer be triggered. It's much easier than the cat variation of getting the key, but also much trickier to find.
21. Head back to the servants' quarters at last and show Hyde the "Pair of Throne Keys." He will follow you.
22. Take him to the throne room. He will sit to the side and wait while you use the keys on the throne. They keys can only be used while you are sitting in the throne.
23. Erol will barge in on the scene and demand you both to stop. He will start to advance towards Hyde, so you must use the "Kitty" on him before he reaches Hyde. If you stand between them you'll have infinite amount of time to switch your items around.
    NOTE: Failing to intercept Erol before he reaches Hyde triggers a Game Over ending that does not count towards any of the recorded endings. So be careful!
24. Hyde will ask Monica to come with him, so pick "Of course!" to continue on with the ending.
    NOTE: Picking "I can't..." will once again trigger a game over the does not count towards the recorded endings.
25. You'll be in the catacombs now. Step on the other switch to lower the gate and trigger the ending.

There is a large variation to Hyde's ending if you are able to remove Gilroy from the servants' quarters before giving the keys to Hyde. This will cause Gilroy to not tell Erol about the thief and so the entire confrontation between Erol and Hyde will not occur. This is the only route in the game that will actually show you inside of the treasure room.

Complete Steps 1-20 as above; however, do not show Hyde the "Pair of Throne Keys."

21. Head downstairs to the empty guest room and take the "Mop."
22. Give the "Mop" on Gilroy and he will follow behind you. Take him to the dining room.
23. While Gilroy is cleaning diligently, talk to Hyde and he will tell you that he thinks Gilroy has a crush on you.
24. Talk to Gilroy and try to ask him about this, but Reva will break up the moment. She has ordered Gilroy to clean the dishes.
25. At this point, do not follow Gilroy to the kitchen, and instead head back to the servants' quaters. Hyde has returned there, not wanting to ruin his fingers washing dishes, I'm sure. You can now show him the "Pair of Throne Keys" without worry of Erol showing up. Hyde will follow you.
    NOTE: For added sting, you CAN follow Gilroy to the kitchen and initiate the scene where you wash dishes, head back to the servants' quarters and talk to Gilroy again. During the conversation with Reva, fail to defend Gilroy by picking "I'm sorry for getting in the way, I'll leave now," or "Gilroy, how could you steal Daddy's sacuer?" depending on if you took the "Golden Saucer" while cleaning the dishes or not. This will have Gilroy thrown out of the castle and you can carry on with Hyde by showing him the keys.
26. Take him to the throne room. He will sit to the side and wait while you use the keys on the throne. They keys can only be used while you are sitting in the throne.
27. The two will head to the treasure room and Hyde will ask Monica to come with him, so pick "Of course!" to continue on with the ending.
    NOTE: Picking "I can't..." will once again trigger a game over the does not count towards the recorded endings.
28. You'll be in the catacombs now. Step on the other switch to lower the gate and trigger the ending.