Detective Inspector Max Arnold lives on a battered houseboat at the end of Cheyne Walk after separating from his art dealer wife Astrid. The son of a local bookshop owner, Max is a far cry from the affluent elite whose crimes he’ll help solve along with D.C. Priya Shamsie.

Orbiting a quiet backwater planet, the massed forces of the universe’s deadliest species gather, drawn to a mysterious message that echoes out to the stars. And amongst them, the Doctor. Rescuing Clara from a family Christmas dinner, the Time Lord and his best friend must learn what this enigmatic signal means for his own fate and that of the universe.