At an 1847 revival of Meyerbeer's opera Robert le Diable, the ghost of Blaise Thibodeaux, the author of La Résonance du temps, appears in one of the boxes, just as Thibodeaux had predicted to Auguste Dupin that it would, thirteen years before. Unfortunately, Dupin is unable to attend the performance, leaving his uninformed friend and narrator Reynolds to try to make sense of the apparition and all the confusing circumstances surrounding it. Once Dupin has returned to the intellectual fray, however, and pulled the multitudinous threads of possibility together, seven individuals must set forth for the forest of Fontainebleau in the dead of night in order to bring the "temporal resonance" that Thibodeaux had earlier attempted to produce to its full fruition, hoping at least to understand why he wanted to do so—although the Comte de Saint-Germain, apparently in control for once, has much greater ambitions than that... Another riveting entry in this ongoing historical fantasy series.