Midsomer Murders S23E02 - The Debt of Lies

Challis Court seems to be a tight-knit community for retired police officers, but hierarchies from the force have remained--and resentments. When a new arrival is found dead, the other residents regard a murder on their doorstep as an affront and a challenge. Since Challis is a gated estate, Barnaby realizes that the killer is likely a resident… and therefore an ex-police officer.