Di and Neil are now man and wife—but only they and Fenner know that the marriage is purely one of convenience, and after the events of Neil’s stag night, Fenner is understandably extremely uncomfortable when Di starts showing off her wedding photos. There’s another happy couple on G-Wing—Cassie has had a change of heart regarding Roisin’s children and is now comfortable with the idea of living with them. She promises Roisin that she will do everything she can to help her battle for custody of the children.

Snowball receives a shock when she arrives in the library to find Al and Denny moving the shelves and their contents into the corridor. She is relieved when she finds the two books that contain her bomb and conceals them carefully amongst the other books. Now that the bomb is safe, she puts the finishing touches to her nun’s disguise by stealing Barbara’s glasses. She also sneaks into Yvonne’s cell and steals the card that was attached to a bunch of flowers Ritchie sent into her. She doctors the card so that it incriminates Yvonne and explains to Fenner that Ritchie has managed to conceal a gun in Karen’s handbag in order to aid his mother’s escape. Karen can’t believe it when she and Fenner find the gun and, after placing it in her desk drawer, she grabs the radio and orders the POs to track Yvonne down.

HMP Larkhall’s Open Day goes ahead—bit not, of course, according to plan. The Three Julies perform a self-penned protest rap, and Cassie and Roisin make sure that the visitors don’t leave without drawing attention to a few of the flaws in the prison system. Yvonne has grabbed the opportunity to smuggle yet another male escort into the prison and whisks him away to the privacy of Henry’s office. Snowball is waiting for a call from Ritchie and forced to hide under the table. When the phone rings, Yvonne hangs it up when she hears Ritchie’s voice. She then dials 1471 and calls him back to tell him that she’s on to him and Snowball and that they’re both in serious trouble.

Denny and Shaz are delighted to see one another for their inter-prison visit, and jam the lock in the visiting room to ensure their privacy before getting high on magic mushrooms—which means that they are chillingly unaware of the terrible danger they face as Snowball’s bomb finally detonates. Barbara, all three Julies, Al, Buki, Neil, Cassie, and Roisin are all trapped inside the library. When they realise that he is critically injured, Cassie and Roisin make a daring attempt to save Neil’s life. On the wing, Karen does her best to organise the POs while Henry worries about Barbara. Just when it looks like things can’t get any worse, Fenner arrives with news about the fire brigade—they are stuck in a traffic jam en route to the prison.

Karen and Fenner go down to the block to question Yvonne. Karen listens in shock and mounting horror as Yvonne reveals to her that Snowball and Ritchie planted the bomb so that Snowball could escape. Realising that she has been played for a mug, Karen sets off in search of Snowball who is now dressed as a nun and mingling with the other visitors. Luckily, Karen manages to apprehend her just as she is about to step through the gates. An unrepentant Snowball is taken down the block, but Fenner has a surprise guaranteed to wipe the smile off her smug face—five minutes alone with Yvonne.

Julie S and Al manage to break through to Denny and Shaz. But Shaz is still off her face and refuses to leave. Unable to drag Shaz over to the door, Denny is forced to abandon her and make her own escape. The others pull her through the door just as a flaming bookcase collapses. Shaz finally sobers up when she begins to choke on the smoke pouring into the room, she screams for Denny to help her but it’s too late. Upstairs, Fenner tries to persuade Karen not to report the gun—they’ve apprehended Snowball, so why should she risk her job? But Karen has made her mind up and picks up the phone. However, when she opens her desk drawer, she finds that the gun has gone.

The fire brigade has finally arrived but it looks like they might be too late to save the women in the library. As they hang out of the barred window, begging the firefighters to save them, Julie S falls to the floor choking. Over on the other side of the room, Barbara is unconscious with blood trickling out of her ears. Finally, the fire breaks through the door and the room is consumed with flames.