The Snake, the Crocodile, and the Dog - Elizabeth Peters

With Nefret, now a ward of Amelia and Emerson, and Ramses at home pursuing their studies, the couple returns to Amarna in 1898 for a dig that promises to be just like old times. The trip turns out to be more like old times than they plan, however, when they become the targets of a Master Criminal's evil plot. Emerson is kidnapped, and Amelia rescues him to discover that he has lost his memory. Tantalizingly close to her most important discovery yet, a tomb that may have been Nefertiti's, Amelia needs to turn her attention to regaining her husband's love.