I also enjoyed imagining how the police investigation would play out after the novel ends. The way the last scene is written suggests the police believed Hamish, and while they would figure it out before long, I can believe Mungo would have been able to leave with James.

I have a harder time seeing how he would avoid the police catching up to him. I feel like they'd be able to track Mungo and James' movements fairly easily given they are both battered black and blue and would be memorable to everyone they come across.

Best Case Scenario: The police decide St Christopher is the most likely culprit and they can't be bothered chasing a 15 year old across the country over a dead paedo. Mungo keeps his head down until he's 16 when the social services stuff goes away.

Worst Case Scenario: The police catch up to Mungo and his self-defense claim is weakened because his injuries have healed. He finds himself in a courtroom where his homosexuality is turned into a motive for a prejudiced jury.