When Ted Hughes's Birthday Letters was published in 1998, it was greeted with astonishment and acclaim. Few suspected that Ted Hughes had been at work, for a quarter of a century, on a cycle of poems addressed almost entirely to his first wife, the American poet Sylvia Plath. In Ariel's Gift, Erica Wagner provides a commentary to the poems in Birthday Letters, pointing the reader towards the events that shaped them, and, crucially, showing how they draw upon Sylvia Plath's own work.