The Obsidian Chamber

After the apparent death of Agent Pendergast in the previous novel, Constance Greene has returned to Riverside Drive, but Diogenes seems to kidnap Constance, and Proctor pursues them by plane to Canada and Africa and by car into the dessert where he is stranded. As it turns out, the chase was merely a diversion. Constance is still grieving in the basement of Riverside Drive and is slowly seduced by Diogenes, while the surviving Agent Pendergast has been fished out the sea by smugglers who want to use him to free a colleague from prison and plan to kill him at the end.

Agent Pendergast manages to free himself, and just as he is about to return, Constance gives in to Diogenes and follows him to his island. Diogenes tells her that the incident on the volcano changed him and he is now working on two things: Reconstructing the potion that gave Constance such a long life, and making her happy. He even told her he gave up killing, though in truth he seems to have no such inhibitions, as he is perfectly happy to kill some people in order to gain the last ingredient to the potion.

While Agent Pendergast tracks him down through his latest killings, the young women that helped Diogenes fake Constances kidnapping follows him also to the island and is determined to kill Constance as she wants Diogenes for himself.

Meanwhile Constance receives Diogenes declaration of love and explains to him that this was her revenge. Making him fall in love with her and then leaving him. But her decision to leave is first hindered by a murderous attempt of her rival and then by the arrival of Pendergast and the FBI command units.

In the end, Pendergast decides to accept his responsibility in Diogenes development, decides to let him live and go, and even convinces a good friend of his to let Diogenes escape. However, when Constance asks him to love her the way she wants him to, he declines and she leaves him to join her son in the far East.

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