Fan Casting Hayley Shipton in Scales: Mermaids are Real - A Tail of Crime in New York (2015)

A very-spirited independent investigator who was a cop from the London Metropolitan Police Service and an insurance company security investigator but she is actually an agent for MI6 British Intelligence and also works for Castle's PI agency with Castle and his daughter, Alexis. She is also involved in the NYPD 12th Precinct's investigation into Gary Witts and his mermaid hunting activity in which she also serves as Castle and Beckett's Third-in-command.