The Doctor, Constance and Flip join forces with 51st-century bounty hunter, Calypso Jonze, to hunt down the Somnifax: a weaponised mind-parasite capable of turning its host's nightmares into physical reality. Chasing it through the time vortex to Providence, Rhode Island in 1937, they arrive too late to stop it from latching onto a local author of weird fiction... Howard Phillips Lovecraft.