In a grand English country house in 1899, an aspiring art forger must unravel whether the man claiming to be her long-lost cousin is an impostor.

An unwanted guest of her uncle's family since childhood, Grace has grown up on the periphery of a once-great household. She has unusual predilections: for painting, particularly forgery; for deception; for other girls. Her life is altered when a letter arrives from the South Atlantic. The writer claims to be her cousin Charles, long presumed dead at sea. When he returns, a rift emerges between family members who claim he is an imposter and Grace's aunt, who insists he is her son. Grace, whose intimate knowledge of fakes is her own closely guarded secret, is forced to decide who to believe and who to pretend to believe. In deciphering the truth about her cousin, she comes to understand other truths: how money is found and lost, and who deserves to be rich; what family means to queer people; and the value of authenticity, in art and in love.