Verity Jane, gifted app-whisperer, has been out of work since her exit from a brief but problematic relationship with a Silicon Valley billionaire. Then she signs the wordy NDA of a dodgy San Francisco start-up, becoming the beta tester for their latest product: a digital assistant, accessed through a pair of ordinary-looking glasses. "Eunice," the disarmingly human AI in the glasses, soon manifests a face, a fragmentary past, and an unnervingly canny...