When the Doctor loses both Sam and the TARDIS after an encounter with a mysterious dimensional anomaly, he finds himself affected in a very fundamental way, doubting his own powers and making crucial errors of judgment.

Stranded amongst the forests and lakes of southern Sweden in the summer of 1999, it quickly becomes clear to the Doctor and Fitz that something unusual — and dangerous — is afoot. Fitz finds himself acting the hero as the search for Sam gets them involved with investigations into strange disappearances — and manifestations of even stranger creatures.

Events quickly spiral out of control as the Doctor and Fitz become entangled with a secret deep beneath the forest, a secret which could save Sam and an entire doomed alien race — but destroy the Earth in the process.