The following version of the book was used to create this study guide: Denfeld, Rene, The Butterfly Girl, Harper Collins, New York, New York, 2019. Kindle AZW file.

Butterfly Girl, by Rene Denfeld, is the sequel to The Child Finder. Butterfly Girl continues the story of Naomi, a private investigator who specializes in missing children. Her own experience as an abducted child prompted her to focus on this area of her profession. Naomi feels her life is on hold until she finds Sarah, her younger sister who was also kidnapped and whom Naomi left behind when she escaped. Naomi is married to Jerome, a Native American who lost an arm in the war. The two met while they were both in foster care and Jerome is fully supportive of Naomi's quest, even though they are struggling financially and he longs to put down roots. They spend some time with one of Naomi's friends, a woman named Diane who welcomes them into her home and includes them in her life. When Naomi agrees with Jerome that it is time to settle down, the three of them become a family together, living in Diane's house.

Naomi begins investigating a string of murders only a short distance from where she was held captive as a child. She knows that none of the bodies that have been found so far are her sister, but she hopes that the murders will provide her with leads. Naomi soon meets a homeless girl named Celia, who captures Naomi's attention and her heart. While Naomi is focused on finding Sarah, she also begins to get to know Celia. Celia left home when her stepfather, Teddy, began raping her and her drug-addicted mother refused to leave him. She lives on the streets rather than facing the horrors of daily life at home. Though the other street kids warn her of how dangerous it is to become emotionally attached to anyone, Celia finds herself interested in Naomi.

Celia had seen someone in the basement of a house that seemed abandoned, but she does nothing with the information at first. Even though Celia is aware that someone is killing homeless girls, she has no real way of protecting herself. Celia then meets up with a man she (and Naomi) believe to be an undercover police officer, placed on the streets in an effort to find the predator who is killing off kids. Celia tells the man about the house and agrees to show him the location. When they arrive, she discovers that the man is Wesley Thurman, son of a judge who had taught Wesley to be a predator, and Celia becomes his next victim. Celia also realizes the only other person in the house is Sarah, Naomi's sister. Together, Celia and Sarah come up with a plan to escape, but Wesley survives Sarah's effort to poison him. Just as Wesley is facing them with a gun, Naomi arrives, having found a map Celia drew to the house. Naomi enters and Wesley gets off one shot, but Naomi fights back. She has Wesley on the ground, pointing his gun at him, when Jerome arrives with other law enforcement officials. He had followed a separate trail that also led him directly to the house.

As the novel comes to a close, Naomi and Jerome have settled into their new life at Diane's house with Celia as their foster child. Jerome and Naomi are each working on investigations, and Naomi testifies in the case against Wesley Thurman. Meanwhile, Sarah – having spent some 20 years as a prisoner – is in a mental institution where she is beginning to heal and to cope with the world.