Castle and Beckett investigate the apparent robbery-homicide of a New York cab driver, only to discover that the victim was involved in a mysterious conspiracy with unimaginable consequences. As the stakes continue to rise, hard-charging federal agent Mark Fallon takes over the investigation. Together, Fallon, Beckett and Castle must race to unmask the truth about the victim before it's too late.
As their doubts, fears and suspicions grow, Aria, Emily, Hanna and Spencer start to wonder what the true face of evil looks like. Is it the girl who holds a grudge and will do anything to keep her loved ones near? Is it the new brother-in-law who might have a darker side beneath the surface? Or is it an unknown stranger who is playing puppet master with four girls' lives? Only time will tell who the Bad Seed is. Meanwhile, Aria sees the school play as an opportunity to get closer to Ezra. But will her plan backfire and put her relationship in jeopardy?
When Benson takes the night off, Mordecai and Rigby decide to throw a party, but as it gets off on a rocky start, they seek the help of Party Pete to get their party going. But the duo soon learn the hard way that Party Pete is unstoppable when drinking RadiCola.