It is ten years since Harry Sullivan left UNIT and gave up his travels in the TARDIS with the Doctor and Sarah Jane.

Since then he has been engaged in top secret work, developing antidotes to nerve toxins.  But when he is transfrerred to Yarra in the Hebrides to work on weapons research, he has severe misgivings.  For one thing, it goes against much of what he believes in.  For another, someone is out to kill Harry Sullivan.

Who wants Harry safely out of the way?  What significance does a painting by Van Gogh have in the affair?  And can Harry's old friend, the Brigadier, really be involved in a scheme which threatens the security of the Western World?

In the sleepy village of Hazelbury Abbas the Winter Solstice is fast drawing near. It is a time of deep mystery and ancient evil. Sarah Jane Smith, journalist and former companion to the Doctor, comes to Hazelbury Abbas to start work on her new book. While there she meets Brendan, the young ward of her Aunt Lavinia. Suddenly Brendan disappears. Has he been kidnapped by the practitioners of Black Magic who are said to live in the village? Is he to be sacrificed to the goddess Hecate on the Winter Solstice? But Sarah is not alone in her search for Brendan. Across the unimaginable gulfs of time and space, the Doctor has sent her a very special companion: a robotic dog by the name of K9...

Of all the companions ever to travel with the Doctor in the TARDIS, Turlough was the most enigmatic and the most disturbing. Exiled from his home world, he saw the Doctor as a means of escape from Earth - and for that he was prepared to kill. But just who was Turlough? And what happened to him after he left the Doctor? Now Turlough has returned to Trion, but to a Trion much changed since his exile. Who are the mysterious Gardsormr? What is their secret purpose? And what is the shocking and terrifying link between Trion and planet Earth?