Here is the official description for Castle season 7 episodes 18, "At Close Range" - airing March 23rd.
Season 7 Episode 18 "At Close Range"
Detective Kevin Ryan is on the security detail of a charismatic congressman attending a charity event when shots suddenly ring out. Driven to apprehend the killer, Ryan must revisit the events that led up to the shooting, with the help of Castle and Beckett.
Nathan Fillion as Richard Castle
Stana Katic as NYPD Detective Kate Beckett
Susan Sullivan as Martha Rodgers
Molly Quinn as Alexis Castle
Penny Johnson Jerald as NYPD Captain Victoria Gates
Tamala Jones as Medical Examiner Lanie Parish
Jon Huertas as NYPD Detective Javier Esposito
Seamus Dever as NYPD Detective Kevin Ryan
guest & recurring cast:
Maya Stojan as Tory Ellis
David Conrad as Frank Kelly
Reiko Aylesworth as Mia Lopez
Ricardo Chavira as Alex Lopez
David Andrews as Carl Shelton
Annie Little as Carolyn Decker