Den of Liars by Jessica S. Olson

Here is a summary with spoilers for Den of Liars by Jessica S. Olson

Lola St. James is the world's best-kept secret. When her father’s loss in the Liar’s Dice Tournament—a high-stakes competition where players are forced to gamble with their deepest secrets—made her a target, she was rescued by the Thief, the notorious leader of the Tentacles. Enzo gave her a choice: her heart in exchange for protection. Years later, Lola and Enzo are best friends, especially since she gave him her heart and their emotions are connected. On top of that, she is still hidden from the world, as everyone believes her to be dead, including her father. The two spend their time thieving together, although Enzo has never offered Lola a permanent spot as a Tentacle.

Enzo has a curse: in order to live, he must steal soulight. He is tired of living that way and believes his answers—and the cursebreaker—lie in finding a moonshard. However, he thinks there is only one person who knows where it is: his brother, the Liar’s Den Casino owner (Nic, although Lola is not given that name). Since Nic does not know Lola, Enzo sends her in to steal a voratium pocket watch linked to the moonshard’s secret. The job goes wrong, and Lola barely escapes, confronting Nic, whose magic lets him sense lies and bend reality. Fascinated with each other, they clash, and Nic tempts Lola into the Liar’s Dice Tournament with the promise of an Unbreakable Lie—a deception powerful enough to rewrite her past.

Lola talks to Enzo to see if she should enter, and though he is hesitant, he tells her to be safe and do it. She officially enters, but in order to do so, she must wager a secret that the Liar will know if she fails the game. She tries hard to pick a safe secret, but he ends up getting the one that ties her to Enzo. Thus, Lola’s first task for the game is to lie and steal the watch from Dr. Legrand. Lola hates the lies and deceit she tells Dr. Legrand, because she sees her as a friend, and her guilt quickly overwhelms her. Soon after the first task, Lola passes out and the Liar takes her back to her room to recover, shifting their enemies-to-something-more relationship into motion.

Her next task becomes more personal when she learns she must lie to the man who covered up her own death. During this time, Nic starts to realize who Lola is. Lola also learns more about her past, while her friends begin warning her that Enzo might be lying to her. But every time she starts to doubt him, Enzo shows up (thanks to her heart), and she manages to forgive him all over again.

After a confrontation with the Liar, the two start talking again and decide to play a game of truth or dare. By the end, they have shared many secrets, from their real names to Nic’s relationship with Enzo and an old fling named Laura. When things get too vulnerable, Lola runs away, but Nic feels cheated and lied to. He tries to put the Liar mask back on, but Lola hates that he hides behind it and calls him out, which leads to them kissing. Later, Enzo finds out what secret she bargained away, and he is furious, leaving Lola to question how much she trusts him again.

Lola’s world begins to unravel. She learns that Enzo did lie, that her father truly did love her, and that she never needed protection from him. She is still uncertain about Nic. However, the Liar’s game must continue, and while she thought she and Nic were fine, she learns her next task is to lie to Enzo and convince him the moonstone is gone. Furious at Nic, she reluctantly agrees. It breaks her heart, but she manages to lie to Enzo and tell him it has been destroyed. Her lie almost works, until she slips up and uses Nic’s name, making Enzo realize that the two are far closer than he thought. Nic eventually appears, and a fight erupts among all three—trust shattered on every side. Enzo drags Lola out, only for her to call him out on his lies and declare that all trust is broken, that she doesn’t want to see him again.

After some time to reflect, Lola wants to return to Nic, but he has used magic to ban her from the building. She then discovers that not only does she have access to Enzo’s magic, but also to Nic’s, and she sneaks in. The Liar’s Tournament is nearly over, but there is one final dice game. Since she is still a contestant, she gets to play, despite Nic’s objections. Lola wins the whole tournament and gains the Unbreakable Secret. Still, she wants to talk to Nic. She knows he doesn’t trust her, so she offers herself up—every secret of hers open to him. Even though he looks, he still doesn’t trust her motives. With no other choice, Lola creates her own game, a new plan where she can reclaim her past and write a better future. She goes back to Enzo, who is ready to take her in again, including as part of the Tentacles—just the first step of her master plan.