Derek has been teaching Debbie to drive, but it hasn't been going well - and now she's been seeing a mysterious man in her lunch hour. Paranoid that his girlfriend is cheating, Derek takes up the post of mall security guard, which allows him to keep an eye on her. But Derek is a useless security guard; he mistakes a burglar for a window cleaner, and allows the crook and his team to help themselves to Karen's precious new laptop. Not only that, Derek also manages to handcuff TJ and Karen together - and then lose the key. The pair are reluctantly condemned to each other's company all night, until the key turns up in one of the Christmas crackers the next day. Debbie reveals to Derek that the mysterious stranger is only a driving instructor.