'The boy looks about seven or eight years old and should weigh next to nothing. And yet it takes four men to drag him out of the water. We soon realize why. Padlocked around his ankle is a thick metal chain, which plummets right down to the sea's bottom. If we want to save him, we have to pull up the chain. And whatever is at the end of it.' Silas Orr, an 11-year-old runaway from Greenock, is saved from certain death by Captain Jon Harkin,...