A biopic about Louis Wain, an English artist who lived between 1860-1939 and is best known for his drawings, which consistently featured anthropomorphized large-eyed cats and kittens. In his later years he may have suffered from schizophrenia (although some specialists dispute this claim), which, according to some psychiatrists, can be seen in his work.

At the age of 23, Wain (Benedict Cumberbatch) married his sisters' governess, Emily Richardson (Claire Foy), who was ten years his senior. The marriage was considered somewhat scandalous at the time due to the age difference. He moved with her to Hampstead in north London but Emily soon began to suffer from breast cancer and died three years into their marriage. Prior to Emily's death, Wain discovered the subject that would define his career. During her illness, Emily was comforted by their pet cat Peter, a stray black and white kitten they had rescued after hearing him mewing in the rain one night.

Despite his popularity, Wain suffered financial difficulty throughout his life. He remained responsible for supporting his mother and sisters and had little business sense. He often sold his drawings outright, retaining no rights over their reproduction.