The Obsidian Chamber

The Obsidian Chamber is a suspense novel authored by Douglas Preston and Lincoln Child, published on October 18, 2016, through Grand Central Publishing. It represents the sixteenth entry in the Special Agent Pendergast series.

Plot

After Agent Pendergast's presumed demise in the preceding book, Constance Greene returns to Riverside Drive but appears to be abducted by Diogenes. Proctor follows their trail across Canada, Africa, and into a desert, eventually becoming stranded. This pursuit is a ruse: while Constance mourns in the basement of Riverside Drive, she gradually falls under Diogenes's influence. Meanwhile, the surviving Pendergast is rescued at sea by smugglers who plan to use him to liberate an associate before killing him.

Pendergast manages to escape and readies himself for a return, but Constance tracks Diogenes to his island. There, Diogenes discloses that he is recreating the elixir that prolonged Constance’s life and asserts he has ceased killing—though he continues eliminating those who block his search for the potion’s last component.

As Pendergast follows Diogenes through his string of murders, one of Diogenes's jealous accomplices shadows them to the island with intentions to kill Constance.

Constance admits her love for Diogenes as part of a revenge scheme—to make him fall in love with her and then abandon him. Her efforts to escape are interrupted by an attack from her rival and the arrival of Pendergast and FBI agents.

In the end, Pendergast takes responsibility for Diogenes's actions and permits him to flee with assistance from a trusted confidant. When Constance asks Pendergast for love on her conditions, he declines, prompting her to leave for the Far East to reunite with her son.