Kate Beckett (Stana Katic) will have a blast-from-the-past moment, while her husband Rick Castle (Nathan Fillion) contemplates a decision that will affect their relationship in the next episode of "Castle" season 8.

In the episode titled "Fidelis Ad Mortem," Beckett will go back to the New York Police Department Academy, where she trained to become a police officer, to investigate the murder of recruit officer.

This could possibly feature several flashbacks to her old days as an NYPD Police Academy trainee as Beckett searches for the person responsible for the murder.

Meanwhile, Castle will have to make a decision that could have a great effect on his and Beckett's relationship.

In the first half of season 8, Beckett decided to leave Castle in order to dig deeper into her LokSat investigation. But the two managed to patch things up in episode 8, but they have to keep their relationship a secret so it will not compromise Beckett's cover for the investigation.

But according to the synopsis for the upcoming episode, it seems like Castle has to make a decision of his own regarding the status of their relationship.

This could either mean that Castle already wants to make everyone know that he and Beckett are already back together, or he could be contemplating about running away from their relationship because he wants both of them to be safe.

The official synopsis for "Fidelis Ad Mortem" reads:

"When a recruit officer at the NYPD Academy is killed, Beckett and the team go back to their old training ground to investigate. Meanwhile, Castle must reckon with a decision with profound consequences for him and Beckett."

The episode features several guest stars such as Michael Bowen, who portays the role of Sergeant Joseph Ortiz, Evan Adrian, who will play the role of Bardot, and James Morrison as Commissioner Malone.

"Castle" season 8 episode 15 airs on Monday, March 21, on ABC.