The Castle of Creepiness!/Measle and the Mallockee

After double-crossing wizards lock up Measle's mum and dad, Measle must protect his baby sister and hide with his little dog Tinker. They take refuge in Caltrop Castle, which has huge bolted doors to keep out the lurking horrors. However, Measle soon discovers that the horrors may already be inside the castle itself. This is the third book in the Measle series.