Murder in Mind - Season 3 Episode 5 Contract

Three city dealers' scheme to siphon off money from their company's accounts is suspected by Simon's boss so he and his friends hire ageing hitman Terry Cameron to do away with him. Cameron requires payment only on completion of the job, but when the boss publicly dies of a heart attack the dealers decide there is no need to pay the hitman. Cameron then starts killing the dealers one-by-one as a penalty for non-payment.