The Theft Before Christmas by Cheryl Bolen

When the theft of the Regent's Michelangelo has the potential to set off on international incident, he believes his best chance of recovering it before the donor's Christmas Eve visit is to bring in his favorite investigators: Captain Dryden and his wife Lady Daphne.
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With her usual deft touch, Bolen mixes real historical figures with her own memorable cast of characters. Mix a locked room puzzle, a tour of Regency London, a murder, and a sweet romance between two friends thrown together by Daphne and Jack's investigation, and you have another charming Regent Mystery for the holiday season.-In Print