The clue to a murder in the art world of contemporary Madrid lies hidden in a medieval painting of a game of chess.
In the 15th-century Flemish painting two noblemen are playing chess. Yet two years before he could sit for the portrait, one of them was murdered. Now, in 20th-century Madrid, Julia, a picture restorer preparing the painting for auction, uncovers an inscription that points to the crime: Quis necavit equitem? Who killed the knight?
But as she teams up with a brilliant chess theoretician to retrace the moves, she discovers the deadly game is not yet over.