It is 1931. Iris (Tuppence Middleton, Inspector Lewis) is the darling of her social circle. While on holiday with friends in the Balkans, Iris decides to escape her friends’ raucous partying and travel home to London alone. Her expectations of peace are short-lived when she faints on the platform of the railway station in the scorching heat. She wakes in time to be rushed on to the train but with a pounding head and the feeling of being on the verge of a dream.
Finally seated, Iris is comforted by Miss Froy (Selina Cadell, Doc Martin), whose tweed suit and bookish looks belie a jovial and adventurous spirit. Comfort soon turns to horror when Miss Froy mysteriously disappears. With only the support of the infatuated young engineer Max Hare (Tom Hughes, Silk), Iris maintains the conviction that Miss Froy has somehow been abducted. But who would want to snatch a seemingly harmless Englishwoman?
As fellow passengers refute Iris’ story and threatening figures emerge to disprove Miss Froy’s existence, Iris’ unswerving certitude takes on the appearance of madness, and she finds herself struggling for her sanity—and for her life.