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

Since then he has been engaged in top secret work, developing antidotes to nerve toxins. But when he is transferred 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?