Carmarthenshire County Museum is a slice of history in itself. The building that houses it has been in continuous use since the 13th century, once a Bishop's palace it was where the Bible was first translated into Welsh. But could it also be home to some mysterious cases of mistaken identity and two lost paintings from the time of Charles II? Dr Bendor Grosvenor and Emma Dabiri travel to Carmarthenshire to investigate two intriguing portraits of a local nobleman and his wife, the Earl and Countess of Carbery, possibly painted by the great Sir Peter Lely in the 17th century. Yet all is not as it seems: Bendor has a hunch that one of the portraits is by another hand. Could the portrait of the Countess be a lost work by Mary Beale, Britain's first commercially successful female artist? While Bendor gets to grips with the badly damaged portrait of the Earl, Emma traces the story of how he survived the Civil War, how Mary Beale was written out of the history books, and discovers how the cross-dressing men of the Rebecca Riots stormed Carmarthen.