The following version of this book was used to create this guide: Shapiro, Dani. Signal Fires. Alfred A. Knopf, 2022.

Shapiro's novel is divided into 11 chapters, each taking place on a specific day, with several sub-chapters within, each named after the character that the chapter will be written from the perspective of. Each character is a member of either the Wilf (Ben, Mimi, Sarah, Theo) or Shenkman (Waldo, Shenkman, Alice) family.

In August of 1985, Sarah and Theo Wilf, teenagers at the time, are driving; Sarah, 17, has been drinking, so she gives the keys to Theo, 15, who does not have his license. He crashes the car outside their house, killing Misty Zimmerman, the girl they were riding with.

Then, on December 21, 2010, Ben, the Wilfs' father, is spending his last night in his home before his planned move to a retirement home where his wife, Mimi, is staying; she has Alzheimer's. He sees Waldo, the young boy who lives next door, through his window, and they meet outside their house. Waldo shows Ben an app on his iPad that shows him the constellations in the sky. Waldo returns home, and Shenkman, his father, reprimands him for his passion for the stars and for sneaking outside. Then, perspective shifts to Sarah as she is driven to Ben's house to help him move. Meanwhile, Theo works at his successful restaurant in Brooklyn when he receives a call from Sarah, later that night, saying that their mother has disappeared from the retirement home; he departs for the house to help them look for her. Waldo, upset from his father yelling at him, grabs his iPad and runs away from home to the parking lot of a nearby store that sells swing sets. Mimi walks along the road, disoriented, believing she is looking for her missing children; coincidentally, she encounters Waldo in the parking lot, and she believes he is Theo. She falls and begins bleeding, but Waldo shows her constellations on his iPad to try and calm her.

The novel moves back to New Year's Eve of 1999. Alice, Shenkman's wife, is pregnant with Waldo; her water breaks. Ben, their neighbor, notices the commotion and asks if everything is okay. Shenkman describes the situation and Ben, a doctor, springs into action, going over to help deliver the baby. Waldo comes out with the umbilical cord around his neck, but Ben deftly maneuvers him to safety. Simultaneously, Sarah is throwing a party in Los Angeles, where she works and lives as a successful film producer in Hollywood, married to a struggling screenwriter named Peter. Theo unexpectedly arrives; she hasn't seen him in five years because he went away to South America to work as a chef. The next morning, Theo tries to cook breakfast for the family, but sets off the alarm system by accident, interrupting him. At the same time, Ben arrives home, and Mimi comforts him from the stressful birth before Theo calls. The two entreat him to come home. Newborn Waldo hears his parents conferring about the close call of his birth.

Briefly, the action shifts back to August, the night of the car crash. Ben is upset that he moved Misty despite her neck injury, believing he may have caused her death. Theo and Sarah both assume the blame, and Mimi prays that everything will be okay.

In the early morning of December 22, Theo meets Sarah at Ben's house, and they look for Mimi. Ben remains unaware that anything is wrong. Simultaneously, Shenkman discovers Waldo is missing. Sarah is concerned that the man she is having an affair with will reveal himself to Peter, and the two siblings go in the house to tell Ben what is happening. Mimi begins to see visions of her life flashing before her eyes.

Action briefly shifts to May of 2020. Shenkman tells Waldo, who is home from college due to the COVID pandemic, that he has to sell the house. We learn Mimi died with Waldo that night outside the mall, and Waldo has maintained a correspondence with Ben in that time; he asks him to meet up.

Back in the early morning of December 22, Ben is driving with his children, and the retirement home calls and tells them where they found Mimi's tracking device -- not far from the mall. Shenkman and Alice drive looking for Waldo, and Shenkman's college friend / rival, Lindgren, calls them, saying that Waldo frantically emailed them saying he was outside the mall. Sarah, Ben, and Theo arrive at the parking lot, and Theo correctly intuits that his mother was probably drawn to Play Heaven, the store that sells swing sets. They look inside a playhouse outside, and they find Waldo with Mimi's body. Shenkman also intuits that Waldo will be attracted to Play Heaven, so he drives up to find the Wilfs gathered around. Waldo is able to explain what is happening to his concerned parents. The Shenkmans drive home, vowing to change their lives.

Now, on the night of the car crash in 1985, Ben walks around the neighborhood, reflecting on how close his children were to dying themselves.

In November of 2014, Theo has opened a second restaurant. Ben has moved to Los Angeles to be with Sarah. Sarah has gone to rehab, successfully conquering her alcoholism; she remains with Peter and their two children. Waldo learns that his mother, Alice, is dying of cancer, and calls Ben.

The timeline shifts forward to July of 2020. Shenkman has moved to Florida and reflects on how he failed as a father. Theo's restaurants are closed because of the pandemic, but Sarah's two daughters are coming to help him feed people nevertheless. Waldo drives cross-country to visit Ben and tells him he saw a vision of Mimi's whole life when she died.

Finally, in June of 1970, Ben, Mimi (pregnant with Theo), and Sarah walk up to their new home where most of the action of the novel takes place.