Graeme also created several other series characters such as the team of C.I.D. Superintendent William Stevens and Inspector Pierre Allain of the Surete Nationale, beginning with A Murder of Some Importance in 1931. Twelve more Stevens/Allain novels followed until 1943, including Mystery on the Queen Mary from 1937.
Inspector Pierre Allain is described as a plump, bearded man with dark brown eyes. Although likeable, he possesses a mercurial temperament and claims to be the best detective (and the greatest lover) in France. He dislikes simple cases because they are "beneath" his prodigious talents and don't offer the chance to get his accustomed adulation after solving the affair. Superintendent William Stevens is tall, broad-shouldered and in good shape from exercise that has left his "flesh healthily tinted." Unlike his colleague, he's a family man and less egotistical, but not without his own flights of fancy and the occasional bout of flirting with the ladies.
Robby MacKay, a young shipyard worker who is one of many helping to prepare the Queen Mary get ready for her historic maiden voyage, overhears a scheme to hide something somewhere on the ship, masterminded by a man with a foreign voice. Robby later survives a violent attack and near-drowning to seek the help of the police. Inspector Stevens uses his influence to get Robby a job aboard the ship so he can mingle with passengers and hopefully ID the mystery voice. Meanwhile in France, a dying foreigner with ties to jewel thieves leads Inspector Allain to also snag a ticket aboard the Queen, and soon the detective duo realize the two mysteries are in some way connected.
As Leo Harris notes in his Foreword to a 1992 reprint, though presented as a detective thriller, this is "really a floating Grand Hotel replete with interlocking dramas, romances and comedies, with the msytery element almost secondary. You can enjoy it for its variety of incident and especially for an obliquely revealed view of life in the 30s."