Ep 18. The Wild Rover

In Castle season 5 episode 18, titled "The Wild Rover," Richard Castle (Nathan Fillion) and Kate Beckett (Stana Katic) investigate the murder of a young woman, whose body has been found in the trunk of a car that belongs to an Irish mob boss. The victim, a nurse named Siobhan O'Doul, had apparently been dating the mob boss's son, Liam Finch.

As Castle and Beckett delve deeper into the case, they discover that Siobhan was actually an undercover cop, working to bring down Liam's father and his criminal enterprise. They also learn that Siobhan was planning to leave the force and start a new life with Liam, but her plans may have led to her untimely death.

Meanwhile, Castle's daughter Alexis (Molly Quinn) is dealing with her own problems when her boyfriend Pi (Myko Olivier) decides to become a "freegan" and live off the grid. Alexis wrestles with how to reconcile her feelings for Pi with his unconventional lifestyle.

As the investigation progresses, Castle and Beckett interview Siobhan's colleagues and friends, including her partner in the undercover operation. They also meet Liam's mother, Maeve Finch (guest star Fionnula Flanagan), who reveals a shocking secret about her family's past.

With time running out to solve the case before Liam is indicted in his father's criminal enterprise, Castle and Beckett race to uncover the truth and bring Siobhan's killer to justice. Along the way, they face danger and unexpected obstacles, testing their partnership and their commitment to each other.

"The Wild Rover" is a thrilling episode that showcases Castle and Beckett's investigative skills and their dedication to justice. It also explores the complexities of family relationships, loyalty, and the sacrifices that law enforcement officers make to keep their communities safe.