if you got the key from her use it on the locked door.

You talk to Vincent & he will give you the archives key. You go to the last door in the hallway & you use the key in the brownish looking room... Then you look around in the archives room & get the garden key. Then you go to the room that you talk to Renon in & go through that door. Then you see the garden. When you enter the Garden, go straight until you see that tower looking thing with the torch on the stairs, before you reach it, take a left & go straight, you meet Malus in the entrance. Then you follow him... Now you have to play the game & find out.