John Keenan is a fictional character from the British police drama HolbyBlue, portrayed by actor Cal MacAninch. John is a detective inspector in the Criminal Investigation Department (CID) of Holby South police station. MacAninch was involved in a long casting process for the role, but liked playing a police officer as his brothers are policemen. The character is billed as "fearless" and "straight-talking" with a dedication to his job that damages his marriage to Kate Keenan (Zöe Lucker). John's backstory is explored in series two through the introduction of his abusive father (Kenneth Colley).