Sarah Jane leaves Luke with Clyde's mother Carla while she leaves to pursue an alien called Travist Polong. Meanwhile, Rani discovers that Jacob, a student at her school, has obtained a pendant that grants the wearer mind control powers but slowly turns him into a monster. Frightened of its evil power, Jacob throws the pendant away. With Sarah Jane gone and Mr. Smith shut down, Rani leaves the pendant in Sarah Jane's attic for safekeeping.
Clyde's Disappeared Dad Paul suddenly returns to his family after a five-year absence in which he ran off with Carla's sister Melba to Germany. Clyde and Paul go for a walk, hoping to get reacquainted. Hoping to impress his father, Clyde takes him into Sarah Jane's attic and shows off the alien technology they've found. The pendant calls to Paul, convincing him to steal it. Clyde and Paul leave Sarah Jane's house and run into a suspicious Haresh. While talking to him, Paul figures out the pendant's powers and tells Haresh to keep doing pushups. They are then confronted by Rani and Luke. Paul forces Clyde to forget Rani and Luke with the pendant and leaves with him. Haresh is left doing pushups, risking dehydration.
Paul and Clyde go on a shopping spree, using the pendant to get free clothes and an expensive sports car. Because Sarah Jane is in a building with no cell phone reception, Rani and Luke contact Maria and Alan Jackson. Alan finds out that the pendant will eventually turn Paul into a dangerous creature called a berserker. Alan then hacks into a UNIT tracking satellite. Using Clyde's cell phone number, they are able to track down him and his father. With Carla's help, they pursue them to a marina, where Paul hopes to steal a yacht and travel the world. When Clyde expresses reluctance at leaving his mother, Paul tells him to forget her too. By now, the pendant has almost completely taken Paul over. Being forgotten, Rani, Luke, and Carla are unable to get Clyde to listen to them. Fortunately, Sarah Jane shows up after receiving a message from Alan. As Clyde still remembers her, Sarah Jane gets him to trust his friends and mother. Together, Clyde and Carla try to reawaken Paul's memories of them. Sarah Jane takes out her compact and shows Paul his reflection, now deformed by the pendant. This restores Paul's old personality, undoing the Berserker's commands.
Clyde, Carla, and Paul have one last talk by the water. Clyde contemplates forcing Paul to stay with the pendant, but both know that he won't. Clyde uses the pendant to get Carla to forget everything that she learned about aliens and Clyde's adventures fighting them. Paul reveals that he ran away from Melba because she had become pregnant. Clyde tells him to go back to her, saying that he doesn't need him anymore. Clyde then throws the pendant into the water.
- Adult Fear: Imagine your relationship with your son is fine in the morning, and then in the evening he doesn't know who you are...
- Big Damn Heroes: Sarah Jane.
- Calling the Old Man Out
- Continuity Nod: Paul mentions the Daleks.
- Disappeared Dad: Paul.
- Foreshadowing: Sarah Jane mentions how much she'd like to see her parents again. Guess what happens in the next story.
- "I Know You're in There Somewhere" Fight
- Mind Rape: The pendant's powers.
- Shout-Out: Using the pendant, Rani tells her father to impersonate Bianca Jackson from EastEnders.
- The Bus Came Back: Maria and Alan.
- "Well Done, Son!" Guy: Clyde.