The Heavens by Sandra Newman

New York, 2000. Kate and Ben meet at a party and fall instantly, irrevocably in love. Around them, the city glows. It is the first year without a war anywhere. A woman is president, and an air of camaraderie permeates the streets of Manhattan. Kate falls asleep, knowing she is loved. London, 1593. Kate wakes as Emilia - the mistress of a nobleman - and finds the plague at her door. Afflicted by premonitions of a burnt and lifeless city, she sets out to save the world. Each decision she makes will change her life with Ben for ever. A story of love and alternate universes, madness and time travel, 'The Heavens' is a dream bound up in a strange awakening; it is a novel of what we have lost, and what we might yet be able to save.