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.
This is another in the series of original adventures for the Eighth Doctor.