The protagonist, Zette McGee, had been a police detective until unwanted dreams--or memories--made her suspect that she wasn't the person she'd always thought she was, but was instead a highly sophisticated disposable android, without any human rights. At that point she retired to a distant planet where nobody knew her, and where she made only one new friend, an elderly gentleman named Gideon Smith, who respects her privacy and has a wealth of secrets of his own, which he reveals on occasion when one of his strange abilities or areas of knowledge can help Zette.

Zette's retirement is interrupted when she gets a call for help from a fellow "disposable", who claims to have known her long ago, before they were activated and sent out into the world. She has no memory of him, but her own curiosity and the habits of a policewoman push her to investigate his case, even when he is killed before she can speak to him. The situation escalates, constantly increasing in scale, until Zette is hired by one superhuman intelligence to investigate another, and she learns many secrets, including explanations of the "loose ends" mentioned above.

The story is thus a private investigator's journey into levels of intrigue far beyond those normally encountered by a human--or android--and a discussion of various kinds of intelligent entities, with and without legal status.

Hydrogen Steel is a highly readable and entirely convincing book. The reader is drawn immediately into the reality of Zette's first person narration, and shares her experiences as they unfold.