.. Opening the diary

Lucy hid it in a safe place. ( Use the hotspot key to see all the interesting hotspots. )

The key is guarded by someone.

It is in the treasure chest inside Clive the Piranha's fish tank.

Maybe if Clive wouldn't be so hungry you can stick your hand into the fish tank.

Take some fish food (Pick up) and give it to Clive (Use).

You can now get the key from the treasure chest and open the diary.