How do enigmas and riddles work in literature? This benchmark study investigates the literary trope of the riddle, and its relation to the broader term 'enigma', including enigma as large masterplot. Cook argues for a revival of the old figure of speech known as 'enigma' from Aristotle to the seventeenth century by demonstrating its usefulness. The opening chapter surveys 'enigma personified' as sphinx and griffin, resuscitating a lost Graeco-Latin pun on 'griffin' used by Lewis Carroll. The history and functions of enigma draw on classical and biblical through to modern writing. Wide-ranging examples concentrate on literature in English, especially modern poetry, with three detailed case studies on Dante, Lewis Carroll, and Wallace Stevens. An important contribution to studies of poetic thought and metaphor, this anatomy of the riddle will appeal particularly to readers and scholars of poetry, modern American and comparative literatures, rhetoric, and folk-riddles.