After a married woman decides to meet with an ex-boyfriend she hasn't seen in years, all hell breaks loose when he becomes obsessed with her and wants to become the only man in her life.

Stacey has a good life with a husband and two daughters, but something is missing in her marriage. She loves Chet but things have long since fizzled. With one of her two daughters off to college, Stacey struggles to find meaning in her life. When Chet suggests she use social media to look up old high school friends, she is skeptical at first but decides to give it a try. Stacey reconnects with a few female friends but it’s a man who begins to dominate her thoughts - her high school boyfriend Troy. After giving it some thought, she decides to send him a friend request and see what happens.

The two begin sending each other messages. To Stacey, it is harmless fun to fill a void in her life. When Chet picks a vacation destination at the beach, Stacey realizes that Troy lives in the area. Daydreaming about seeing him again excites her, even though she doesn’t believe she would actually see him.

But Troy consumes her mind. By the time Stacey’s family arrives at the beach, Troy has nearly convinced Stacey to meet him for a cup of coffee for old time’s sake. He nudges her a little further until she agrees. The only way to meet up is while her family is asleep so Stacey sneaks out their first night at the condo and meets Troy at a bar. Old feelings stir for both. With no coffee available, Stacey plays it safe with a soda as they reminisce. Wanting more, Troy talks Stacey into driving him back to his apartment nearby to look at old pictures. When the two come together in a kiss, it’s that moment that makes Stacey realize what a mistake she has made. She loves her husband and wants to work on her marriage.

Only Troy is more devious than she could have imagined. He purposely leaves his wallet in Stacey’s car so he can stop by her condo the next day to get it. With the cat out of the bag, Chet is very upset. He decides to try and save their vacation but his disappointment in Stacey leaves a bigger divide in their relationship.

Upon arriving home, strange things begin to happen. A slashed tire on Chet’s car and Troy in disguise selling candy bars to the other daughter Olivia. When someone robs Chet and shoots him in the head, Stacey starts to suspect Troy and tells the detectives to look at him. Troy has gone missing from his apartment and job, leading Stacey to believe he is stalking her.

While home alone with Olivia, Troy uses a key he got from Chet to enter during the night. He ties Olivia up and knocks Stacey out. When Stacey wakes, she realizes she has to stop Troy. Reasoning with him doesn’t work. She gets out of her ropes and attacks him, suffering a gunshot wound in the process. When Mary, the elder daughter, arrives home, Troy attempts to use her as a hostage. The mother/daughter duo grow victorious in killing Troy. Stacey and Chet both survive their ordeal and decide nothing is more important than working on their marriage.