In 17th-century London, unnatural babies are being born: some with eyes made for the dark, others with webbed fingers and toes better suited to the sea. Sarah Davis is intimately familiar with such strangeness—she herself was born marked by uncanniness. Having hidden her nature all her life and fled to London under suspicious circumstances, Sarah starts over as a midwife’s apprentice, hoping to carve out for herself an independent life. As a member of the illegal Worshipful Company of Midwives, Sarah learns to reach across the thinning boundary between her world and another, drawing on its power to heal and protect the women she serves. When the wealthy Lady Wren hires her to see her through her pregnancy, Sarah quickly becomes a favorite of her husband, the famous architect Lord Christopher Wren, whose interest in the uncanny borders on obsession. Sarah soon finds herself caught in a web of magic and intrigue created by those who would use the magic of the Other World to gain power for themselves, and whose pursuits threaten to unmake the earth itself.