When the cherubic gospel singer Angel Rose confides her suspicion that someone in the Spread the Light evangelism campaign has been diverting the contents of the offering box into his own pocket, Inspector Roger Tearle, Shirley and Thumbs Thorndyke go undercover as volunteers "". . . the Lord knew what He was doing when He sent you to me!"" says Angel Rose fervently, and once again Inspector Tearle proves that he knows his stuff too. He's the only really professional boy detective around and a match for this eminently savable bunch of sinners which includes a thug named Whitney, a preacher with a weakness for horseflesh and a Bible-quoting culprit.