A struggling widow falls in love with an illiterate short-order cook whom she teaches to read and write in her kitchen each night.

This movie is based on the life of revered British writer and philosopher Iris Murdoch (Dame Judi Dench), is a story of unlikely yet enduring love. As a young academic, teaching philosophy at Oxford, Murdoch (Kate Winslet) meets and eventually falls in love with fellow professor John Bayley (Hugh Bonneville), a man whose awkwardness seems in stark opposition to the spirited self-confidence of his future wife. The story unfolds as snippets of time, seen through older Bayley's (Jim Broadbent's) eyes. He recalls their first encounter over forty years ago, activities they enjoyed doing together, and Iris' charismatic and individualistic personality. These images portray Murdoch as a vibrant young woman with great intellect and are contrasted with the novelist's later life, after the effects of Alzheimer's disease have ravaged her. Murdoch's great mind deteriorates until she is reduced to a mere vestige of her former self, unable to perform simple tasks and completely reliant on her at times frustrated yet devoted husband.

Iris, the statuesque dark-haired wife of the wealthy Parisian banker, Antoine Doriot, vanishes into thin air while the latter settles the bill at an elegant restaurant downtown. Furthermore, things will take a turn for the worse, when only a few hours later, much to his surprise, Antoine will receive a disturbing call from a merciless kidnapper demanding half a million euros in ransom in exchange for his abducted wife. As a result, under police surveillance, Antoine will follow to the letter the kidnapper's instructions with the intention to deliver the money, nevertheless, nothing will go as planned. By now, not much is making sense, while the helpless Iris is still missing. What has really happened to her?

England, 1940: When bombs trap eight children in the cellar of their orphanage, their teacher, Miss Shaw, reads them a story. As the tale unfolds, they are magically transported to a timeless, mythical island, where they witness the story of Darkness and Light, and of how their union and their conflict produced the Iris Warriors, the seven colours of the rainbow which imbue the world with colour. As the candles burn low and bombs continue to fall around them, Darkness, like a black widow spider, seeks on the destruction of her colourful children. Miss Shaw and the orphans begin to fear that neither they nor the Iris Warriors will survive the encroaching darkness.