Montmorency is back, but now he must fight an enemy more cunning and deadly than any other he's ever faced. He must fight against himself and the addiction that is destroying his life.

It's been almost six years since Montmorency left prison, determined not to go back to his life in the London slums. He no longer has to steal to support himself – he earns money through investments and skillful gambling, occasionally supplemented by undercover work for the government, as a partner to George Fox-Selwyn, a member of the London upper class. Montmorency has indeed become the man about town that he had wanted to be.

But his most recent trip with Fox-Selwyn has brought unexpected developments. In Turkey he'd discovered drugs and potions that could change his behavior and his mood. Soon he was addicted to them, endangering their mission and their lives. When he gets both of them back to London, Fox-Selwyn contacts his good friend, Dr. Robert Farcett. In the five years that he has known both Farcett and Montmorency, he has stood between them. Neither knows that Farcett is the doctor who experimented on Montmorency's body while he was in prison, trying out a variety of surgical techniques. But now Fox-Selwyn has no choice but to reveal his secret, knowing it could damage or destroy the friendships he has with both men. Montmorency needs the help of a completely trustworthy doctor, because his addiction is beginning to rule his life and to threaten national security. He knows too many secrets and his dependence on the drugs make him vulnerable.

Unfortunately, the doctor is having his own problems. While demonstrating the latest surgical techniques to an audience of medical students and noted doctors, he makes a very public mistake and his patient died a very bloody and unnecessary death. Depressed and guilt-ridden, he vows to give up medicine entirely and contemplates suicide. Unless he can be persuaded to believe in himself again, he will be of no use to Fox-Selwyn or Montmorency.

So Fox-Selwyn arranges for the three of them to take a trip to Scotland. The two others will both benefit from a little peace and tranquility. But Montmorency takes his drugs and Farcett takes his depression and his guilt. It will be a long time before either of them is whole again. And as they board the train for Scotland, none of them realizes that they are embarking on a strange and unexpected adventure, that will throw them together in new ways, showing them things about each other that they have neither known nor expected.