Teacher Mr Petrie continues to act strangely as the pace picks up in the penultimate episode of the crime drama. He visits student Dessie and warns him that ‘we need to stick together…’

But Dessie has his own plan when he takes a gun on a school trip. Is he simply sick of Baxter bullying him, or is Dessie more of a monster than first thought?

Also, we see a different side to Dr Marr when he finds Evie on a lonely moor, and Alan’s new sonar picks up a monster of sorts lurking in the loch.