Dr. Ashley Cosway was a couples therapist who was a murder victim, in the case that Castle and Beckett investigated in "The Double Down". She was murdered by Eric Marx as part of a deal that Jason Cosway, Ashley's husband, would kill Eric's father-in-law Frank Anderson, as neither man would be a suspect in the murder they committed, and each could arrange an airtight alibi for the one the police might think they did.