Examine the cage and use the ACID on it; take the GARGOYLE (L).
Go up the stairs.
Examine the chest of drawers and place the GARGOYLE on it; take the BLUE GEM 2/2 (M).
Examine the door and place the 2 BLUE GEMS on it to trigger a puzzle (N).
Jump the gems to remove them.
To solve the puzzle, move the gems as follows: B to D, J to B, L to J, D to L, I to K, L to J, A to C, C to K, K to I, and I to A.
Go through the newly-opened door.
Take the LADDER (O).
Back out twice.
Place the LADDER under the window (P).
Go up the ladder through the window.