A young woman, suspected of being pop star Mandy Sutton is killed in an alleyway but Lanie quickly finds out that it isn't Mandy but a Claire, look-a-like she used to get past the paparazzi. Beckett asks Mandy to stay "dead" in order to find the killer.
Alexis and Mandy accidentally swap phones at the precinct and Alexis goes to her hotel room to switch. Alexis confesses that she wants to break up with Pi but is afraid what people will say.
When Mandy decides to go out in public, Alexis tries to stop her and follows. Mandy finds out that Claire was paid to take a fake photo kissing Mandy's ex. Mandy thought the photo had been taken when she was drunk and it caused a breakup between her and boyfriend Zac.
Castle and Beckett come to Alexis' rescue when Mandy's other ex, Jesse holds them at gunpoint.
Turns out that Mandy's own mother, Marilyn set up the fake photos to break up Mandy and Zac because Mandy was going to run off with Zac and start a new life. When Claire threatened to tell Mandy the truth, Marilyn killed her.
When a fake story hits the paper linking Castle to his ex-wife Gina, Kate decides to announce her engagement to Rick to the papers.