In 1946, writer Juliet Ashton finds inspiration for her next book in her correspondence with a native of Guernsey, who tells her about the Guernsey Literary and Potato Peel Pie Society, a book club born as an alibi during German occupation.

Remembering childhood stories her grandfather once told her, young physician Natalia becomes convinced that he spent his last days searching for "the deathless man," a vagabond who claimed to be immortal. As Natalia struggles to understand why her grandfather, a deeply rational man would go on such a farfetched journey, she stumbles across a clue that leads her to the extraordinary story of the tiger's wife.