Nigel Patrick plays a suave but dead-serious British narcotics agent in this sporadically exciting crime melodrama. Patrick is determined that the drug traffic will not spread into his territory. He finds an unexpected ally in Joyce Grenfell, an inveterate bird-watcher. Ms. Grenfell aids Patrick in trapping a brother-sister smuggling team (Elizabeth Sellars and Terence Morgan). Apart from the always delightful Joyce Grenfell, Forbidden Cargo is humorless Dragnet material transplanted to the high seas.