Spiderwick Chronicles

Basicly you have to hold out untill your mom cooks the tomato-bomb. This isn't hard. The kids seem to do nicely on their own but mom can't defend herself so keep an eye out for her. After the oven (bomb) explodes Mulgarath appears and you have to avoid him. Just run to the kitchen and go in the little lift. Do the control prompts when asked and you should arrie in the study. Climb over the bookcases on the far left (walk around the pile) and you get a cut-scene. After that you're on the roof. Jump to the left and climb the stairs. After that you get a cut-scene and the achievement unlockes