Spurred by a decades-long interest, Sonnino delves through well-combed and newly released documents in this attempt to identify the Bastille’s infamous prisoner: the Man in the Iron Mask. Voltaire speculated about him and Alexandre Dumas immortalized him, yet the uncertainty surrounding the identity of the man veiled in black velvet continues to enthrall conspiracy theorists and historical detectives three centuries after his death. With a conversational tone and well-chosen excerpts, Sonnino patiently suggests potential candidates and exposes the flaws in his own early theories as well as those of others, before settling on the figure of Eustache Dauger, a loose-tongued valet who was privy to substantial secrets.

Sonnino’s work sheds light on the desperation of ousted English Queen Henrietta Maria and quite intentionally focuses on the influential French Cardinal Mazarin—to conceal Mazarin’s corruption and protect other powerful figures, a particular prisoner remained hidden, his identity scrubbed from documents and his face veiled for the rest of his life. Dauger retains some of his mystery because of a dearth of surviving personal information, but Sonnino’s search allows readers to participate in the fun of unmasking a legendary figure from the era of the Sun King and The Three Musketeers.