It's 1932: Australian-based Scottish adventuress (and surviving twin) Emily Blackwood accepts a commission from Heinrich Vogel, a former dealer of exotic animals in Manhattan. Vogel now lives with his macabre collection of taxidermy in a remote Scottish castle. Emily is tasked with finding a long-lost treasure that Heinrich believes has been hidden within. Instead, she discovers pages from a diary written by his sister-in-law, Hester, who died after falling from the Brooklyn Bridge on the eve of its opening in 1883. Hester's diary leads Emily to an old book, The Birdcage Library, and into a treasure hunt of another kind--one that will take her down a dangerous path for clues, and force her to confront her own darkest secret . . .