The false Lady Keto is loacated at X: 31 Y:57. Here you will have to fight her guards when you've discovered Lord Keto or if you have pledged your allegiance to the false Lord. There is a secret passage at X: 31 Y: 47. After passing through you'll have to fight some more guards. The real Lady Keto is located at X: 21 Y: 43. One problem, though. She is dead. Cast a raise dead spell or use the Necklace of Revival. As soon as you have found and saved both Lord and Lady Keto you will be teleported outside the castle. You can find the false Lady Keto, or Ambersair, in the room down the hall from the door beyond which you found the lady. Observe that the door at X: 33 Y: 42 is a trap.
The secret passage to/from Lord Keto's castle is located at X: 45 Y: 11.
There are a few other places of interest this side of the secret passage.
At X: 33 Y: 30 is a gladiator arena. I won't go into much detail about it, but you can find a sword at X: 48 Y: 28, and a flail at X: 48 Y: 21. I strongly recommend that you walk into all the rooms here. There are more stuff to be found than the ones I've mentioned.
You'll find a locked door without locking mechanism at X: 18 Y: 41. It's a red herring.
At X: 21 Y: 59 is a book of summoning. If you read out loud from it you might succeed in summoning a few nasties, but beware! The reader will be helpless and all other party members confused. That was the worst battle for me in the entire scenario, as my characters turned out to be my strongest enemies. And they constantly tried to hit each other…
At X: 47 Y: 54 you'll find a book entitled "History of Ketonia". Read it. One never knows what might come out of books…
At X: 48 Y: 44 is a secret passage leading to a not-so-friendly cat.
In the room at X: 52 Y: 42 there are some guards that want you to contribute to their welth. Just kill them. Then continue to X: 52 Y: 37. There you should be able to find one metal and one brass key. Just keep walking onto that square until you have them.
At X: 51 Y: 61 there's a locked door where you can use the metal key. Then try the brass key on the door at X: 53 Y: 58.