A painter and womanizer named Heikichi Umezawa has long been obsessed with astrology and alchemy; he is a wealthy but fairly old man from a respectable family, who stills lives in a traditionally run sprawling household. He is finishing his greatest work: 12 large paintings, each depicting a member of the zodiac. As he works in his private studio on the last one, a portrait of Aries, his head is smashed with a blunt object. The murder is curious: it took place on a heavily snowing day, and many of the suspects have solid alibis. Further, when discovered, the room is locked and apparently had been locked from inside - leading to a locked room mystery.