Give My Head Peace S15E04 - Baby Love

Talk of a Troubles amnesty gets Pastor Begbie thinking about all the time he spent in prison. 

He remembers a guy called Donny, who he thought was his best friend. It turned out that Donny was really an undercover cop who befriended Begbie to get evidence against him. He turned Begbie in to the police and sent him to gaol. 

Begbie always vowed to catch up with the 'rat'. Thinking about it makes him angry again, and he becomes determined to track him down. What he doesn't know is that 'Donny' was actually Billy. After Begbie was arrested, Billy grew a moustache. When Begbie got out, he didn't recognise Billy, and the moustache has been his disguise ever since. As long as he keeps it, Billy is safe.