While you are waiting for Hennie, you decide to walk around the house and examine all the windows and doors. Everything is locked, even the back door that Janet entered through! Then she is now being held prisoner...
You see Jopie, the caretaker of Burgershof, enter his little house. Surely he should be able to help you!
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Looking around,you see around one of the pillars supporting one of the balconies grows an ivy plant with a thick stem. Maybe you can climb up with it to get to one of the balcony windows.