When a teleportation experiment goes badly wrong, Nyssa finds herself stranded on the freezing slopes of the Swiss Alps in 1963. But is it mere coincidence that she finds shelter in a snowbound school, haunted by a malevolent poltergeist?

When the Fifth Doctor arrives, Nyssa and the other inhabitants of the school soon discover that the ghost is merely part of a darker, deeper and more deadly game involving rogue psi talents and something else… Something not of this Earth.