Daly and Rawton are seconded to a women's prison run by a friend of Brownlow's after an inmate is savagely assaulted, and things soon escalate when doctors reveal she isn't expected to survive the attack. Suspecting a drugs smuggling operation inside the prison is at the centre of it all, Holmes is sent undercover to get on side with the prime suspects, Rita Davis and Jo Merton. Holmes uncovers a scam by Davis to steal phone cards from inmates to sell them back. Holmes identifies a prison officer she thinks might be responsible, but further investigation reveals she has been blackmailed by Davis to smuggle phone cards in. Holmes has Davis transferred to another wing, allowing her to get initiated with Merton, who brings her onboard with the drugs scam. As she prepares CID for a raid to catch the next shipment, she identifies the real prison officer involved, who is immediately suspicious of Holmes getting initiated so quickly. Will she be exposed before her colleagues can intervene?