The following version of this book was used to create the guide: Mosley, Walter. The Last Days of Ptolemy Grey. Riverhead Books, 2010.

Walter Mosley's novel The Last Days of Ptolemy Grey is written in the past tense and from the third person limited point of view. The novel defies conventional notions of plot, structure, and form by presenting the narrative in a series of often disjointed fragments. These formal patterns and stylistic choices enact the author's overarching themes. The following summary employs a more traditional linear mode of explanation.

Ninety-one-year-old Ptolemy Grey lived in an apartment by himself in Los Angeles, California. Although Ptolemy had family in the area, his great-grandnephew, Reggie, was the only friend or relative who took the time to visit and care for Ptolemy. Then Reggie disappeared for over a week without informing Ptolemy of his whereabouts. One day, when Ptolemy heard a knock on his door, he was certain it was his missing great-grandnephew. However, an unfamiliar man stood behind the door. The man told Ptolemy he was another one of his great-grandnephews, Hilly. Because Ptolemy had recently been robbed by a local drug addict named Melinda, he was hesitant to open the door to individuals he did not know. Finally, he let Hilly inside. Hilly then insisted upon taking Ptolemy to the bank to cash his retirement checks. Although Ptolemy had trouble remaining engaged with his present reality, he quickly discerned that Hilly had robbed him.

After their trips to the bank and the supermarket, Hilly took Ptolemy to his mother Niecie's house, insisting that Niecie wanted an audience with Ptolemy. When they arrived, Niecie introduced Ptolemy to the young orphan girl she had recently taken in, Robyn. Robyn was unlike anyone Ptolemy had ever met and he was immediately drawn to her.

Robyn led Ptolemy into an adjacent room where Reggie's body was lying in a casket. Because he could not recall anyone informing him of Reggie's death, Ptolemy was overcome by shock and distress.

Ptolemy soon learned that Reggie had been married to a woman named Nina with whom he had two children. Though Nina had stayed with Reggie, she had maintained an ongoing affair with a man named Alfred. Ptolemy soon became suspicious of the circumstances surrounding Reggie's death.

Robyn began visiting Ptolemy at his home. During these visits, she helped Ptolemy clean out his squalid apartment. The cleaner and more orderly the space became, the more clear-minded Ptolemy became. He willingly began helping Ptolemy with the cleaning project, determined to confront the buried traumas of his past.

Not long later, Ptolemy began seeing a doctor about an experimental drug treatment for his dementia. The doctor warned that although the medication might help Ptolemy's mind, it would almost certainly harm his body. Ptolemy did not care. He only wanted to be able to think clearly enough to legally appoint Robyn as his sole heir and to discover the truth of Reggie's death.

The longer his treatment went on, the more present Ptolemy became in his reality. Suddenly all of his memories made sense to him. He also began to understand events that had occurred decades prior during his childhood. He realized that his late best friend, Coy, wanted him to pass his stolen treasure on to black individuals in need. He would do this by vindicating Reggie and supporting Reggie's children. He would also fulfill Coy's dying wish by providing for Robyn.

With the help of Reggie's best friend Billy, Ptolemy determined that when Reggie discovered Nina was sleeping with Alfred, he had made plans to move his family to San Diego. Nina then told Alfred. Determined not to lose Nina, Alfred killed Reggie. Ptolemy blackmailed him into a confession. Then the men shot each other. Ptolemy woke up in the hospital. Robyn informed him that Alfred was dead and that the cops were waiting for Ptolemy to recover before arresting and imprisoning him.