The Midnight Library by Matthew Haig

At the age of 35, Nora feels she is a complete failure. In her younger days she showed great promise, but she has allowed fear, anxiety, poor decisions, and the unrealistic expectations of others to squash her true potential. As a result, she has achieved little of real significance in terms of a career or personal relationships. When her cat dies and she loses her job, it is the last straw. Overcome by regrets and …