The Soulmate Equation (2021) is a romance novel by Christina Lauren—the shared pen name of best friends-partners Christina Hobbs and Lauren Billings. Following an unlikely romance fueled by science, the book was an instant New York Times bestseller, and was chosen as a best pick by platforms such as BuzzFeed, Entertainment Weekly, Goodreads, Marie Claire, and Woman’s World. The novel is one of 27 books that Lauren has published—other popular works including Love and Other Words (2018), The Unhoneymooners (2019), and In a Holidaze (2020).

Plot Summary

The Soulmate Equation tells the story of the blossoming relationship between protagonist Jessica Davis (Jess) and geneticist Dr. River Peña. Jess is a single mother in her late twenties who struggles to balance parenthood and her career as a freelance statistician. While Jess is comfortable raising her daughter, Juno, with the help of her grandparents, Pops and Nana Jo, she is unsatisfied with her love life. She has fallen into a rut, spending most of her time with Juno and her grandparents or at Twiggs, the neighborhood coffee shop. She and her best friend, romance writer Felicity Chen (Fizzy), spend their days doing work at Twiggs and scoping out regular patron River—who they initially know as “Americano.” While Jess finds River physically appealing, she is less impressed by his supposedly antisocial, rude, and solemn personality.

However, when Jess and Fizzy find out that River is the head of a matchmaking company, they decide to investigate further. Jess approaches him about it, experiencing an intense physical reaction to his touch that will persist throughout their relationship. River invites her and Fizzy to his company, GeneticAlly, to learn more. A few hours later, an enthusiastic Fizzy drags Jess to River’s office, and they watch a presentation on DNADuo—River’s genetics-based matchmaking platform. Jess is impressed with the technology, which uses over 3,500 genes to match clients based on compatibility. The highest match is the rare and elusive Diamond Match, which has proven mostly accurate in predicting successful long-term relationships.

Although Jess still dislikes River, she decides to send in a spit sample after a particularly bad day. Soon after, she receives a message asking her to return to GeneticAlly. When she arrives, GeneticAlly employees inform her and River that they are a Diamond Match with a score of 98—the highest score the company has ever seen. They proceed to offer Jess $30,000 to date River for the next three months, until the official launch of DNADuo. After consulting Fizzy, Pops, and Nana Jo, Jess agrees to the offer—made all the more appealing by her recent loss of a major client.

Jess holds on to her first impression of River—however, this changes as they get to know each other. On their first date, she is surprised by his charm and humor, as well as his kindness towards Juno—who interrupts their date by walking over to the restaurant, which is next door to Jess’s apartment. Jess’s physical response to River continues to escalate when they participate in a newspaper interview and photoshoot. She concludes that she is attracted to him, and that the feeling is mutual. At a cocktail party, Jess and River share a passionate kiss in public. They consummate their love following another desperate kiss at the hospital—where an injured Nana Jo is residing.

Despite the growing intensity of Jess and River’s love, the former continues to harbor doubts. At times, she worries that he’s only interested in their budding relationship for the fame or money. However, River works hard to assuage Jess’s fears, being attentive to her family and needs. After only a few months, he professes his love for her—right before their relationship hits a potential snag. A few minutes after River’s proclamation, Jess finds out that their match is a fraud. She informs River, despite worrying that he will no longer be interested in her. River tells her he wants to be with her regardless of their match number—which turns out to be a Diamond Match anyway. Jess and River move in together and get engaged two years later, when the former and Juno ask the latter to be a part of their family.