Commander George Gideon of Scotland Yard attended the Fiftieth Criminal Investigation Ball, along with his wife, Kate, and daughter, Penny. It was a formal and elegant occasion and a good time was had by all - but Gideon was aware of many undercurrents present in the room. Meanwhile, there were crimes to be dealt with. Instantly, there was a murder, for which a bicycle with a loose-fitting mudguard likely held a clue. Moreover, a collapsed building had trapped many, and a man serving a sentence in Dartmoor prison, for a crime he had not committed, was about to have an unauthorised visitor. Gideon was also concerned for his officers too, which just added to what sometimes seemed like an overwhelming burden.