Ep 14. The G.D.S.

When a man is found murdered in a park, Castle and Beckett team up with an elite group of detectives from the Global Defense Strategy to investigate. The team, known as the G.D.S., is led by Agent Fallon (guest star Summer Glau) and includes Special Agent Gibbs (guest star Dylan Walsh), forensic psychiatrist Dr. Cameron Lincoln (guest star Kris Polaha), technology specialist Linda Russo (guest star Krista Allen) and tactical expert Matt Gray (guest star Jeff Hephner).

As Castle and Beckett begin to work with the G.D.S., they quickly realize that their methods are unconventional and their tactics are ruthless. While they are able to make progress in the case, they also begin to question whether the G.D.S. is crossing ethical lines in their pursuit of justice.

As the investigation deepens, Castle and Beckett are forced to confront their own beliefs about justice and their roles as detectives. Meanwhile, tensions rise within the G.D.S. team, revealing hidden agendas and personal conflicts.

In the end, the case is successfully solved, but not without consequences. Castle and Beckett must decide whether or not to pursue justice at any cost, and whether or not the ends justify the means.