It's 1932: Scottish adventuress and plant-hunter (and surviving twin) Emily Blackwood, now living in Australia, 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 the castle walls. But instead, she discovers the pages of a diary written by Hester Vogel, 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 . . .