Scotland Yard are being increasingly frustrated after a spate of jewel robberies leaves them baffled. Assistant Commissioner Cecil Parker comes up with a daring plan to plant one of their own in the gang perpetrating these crimes. Esmond Knight ("Borden") is the man selected, and after faking a crime of his own, seeks to fence the jewels and so manages to ingratiate himself with the gang of the always unseen mastermind. The gang are naturally suspicious of their newest member, but luckily he falls in with Lilli Palmer ("Natasha") who knows all the secrets and is desperate to quit the gang... Can he identify and capture this enigmatic criminal and ensure both of them survive? It was Palmer's first English-language appearance and though striking, she is little more than competent - the same can be said for Knight and the drama is stodgily paced with little of note happening until quite an enjoyable twenty minutes when it all comes to quite a sinister head. It's fine, this - cheap and cheerful, but just a bit too sluggish.