Stuart is horrified to discover his trusted driver and friend is the mystery drug dealer the 'Postman', who plans to use him as his inside man at Sun Hill, using incriminating photos and unexplained payments into his bank account to blackmail him. Jo rumbles what is going on, but Stuart's efforts to put matters right just lead to greater danger. A drugs bust is thwarted by a tip-off, and Manson suspects a leak from within the team.