It is the story of Mason's life, though mostly focuses on his sexual activities as a 15 year old boy with various "45 year old slosh-bags from Woolwich".
The book was first revealed in Podtoid 135: This part goes in here.
"He emerged from the the bus and walked across the street. He knew something was going to happen tonight, but as far as he was concerned it was nothing but a friendly visit. He opened the door and slowly stepped up the stairs to the 4th storey flat where he knew she would be waiting. The lift worked, but he wanted the walk to have extra time to calm his nerves. Sweat ran along his brow as his hands trembled along the handrail, moving up and up further defiant of his urge to turn around and go home.
Mason stepped onto the landing and knocked on the door. After several agonising moments, someone opened the door. There she stood: The slosh-bag that would steal his virginity."