Crestfallen Studios

Ok, up until now I've played the game (all 6 episodes) like 4-5 times, each time doing more and more quests (or whatever you call them), gattering items and so on, but now I have a prob. In episode 6, in Estrana (after much solving and what not) I find the door to Lexus (it's in the tomb with the flowers, below where her original grave was, I know all this cuz I've solved it before but forgot) and I don't know where the star key was! So, any ideas??

In the room with this underwater puzzle right above Jopaga's lair, where you got the crescent key. Through the left door, there's a chest you probably opened already, and behind it a pool of water. When the water is on in this room, just swim there and press enter to dive.