Tim (David Spade) has a blind date with Melissa (Lauren Lapkus), nicknamed Missy. Missy is extremely strange, and her odd behavior turns out to be disastrous for Tim. Missy texts Tim as he enters the bar saying that she is a woman in a blue dress, with a meat-head (Joe "Roman Reigns" Anoai) hitting on her. Tim interjects and tries to save the woman, who is pregnant. But turns out that the woman in the blue dress was actually the wife and Missy was using this antic as an ice breaker with Tim. She calls Tim old, and calls out his blonde wig. Tim doesn't drink and Missy is a bit of an alcoholic. She was set up by Tim's grandmother. Missy picks a loud fight with the husband of the woman in the blue dress, claiming he was staring at her (ogling her).. She flashes him a huge knife and is asked to leave the restaurant. Her wild antics result in Tim sneaking out of the restaurant through a window and subsequently dislocating his ankle.Three months later, Tim's company (Credit Of America) is going through a merger and roles are being re-assigned. Julia (Sarah Chalke) is Tim's ex-fiance is dating Rich (Chris Witaske), who is Tim's colleague. So, as a significant other, she is invited to the company retreat in a few days. Nate (Nick Swardson) is the head of HR and has hacked all of TIm's passwords and knows everything about Tim's personal life.Tim meets a beautiful woman, also named Melissa (Molly Sims), at an airport. They connect with much in common and seem to be perfect for each other (They read the same books, they both don't drink). She ends up giving him her number. He begins texting her (including dick pics) and eventually invites her to his work retreat in Hawaii. However, on the plane, Missy shows up, and Tim realizes he had been texting the wrong Melissa. She says that she was about to jump off a bridge when Tim texted her (Tim assumes she was going to commit suicide, but Missy was just about to go bungee jumping). Missy drugs Tim, forcibly giving him a tranquilizer and he awakens later on the plane to her sexual assaulting him by giving him a hand-job.At the hotel, Missy picks up a fight with kids about riding sea turtles. Tim tells Nate about his messed up by texting the whole Melissa this entire time. In Hawaii, Jack Winstone (Geoff Pierson), the new CEO, welcomes everyone. Nate has already bragged to Winstone about the 2nd Melissa who is apparently Miss Maryland and a total hottie. Winstone is eager to meet her, while Tim is anxious not to reveal the truth to Winstone. Tim tells Missy about the brags and asks her to cooperate. Missy is awkward and wild (she give fortuneteller readings to the entire company) and always seems to end up leaving Tim in embarrassing situations (she dances awkwardly on stage in front of everyone, dry humps Tim, bites him, throws food around) in front of his boss and colleagues. Missy gets super drunk and attempts to jump off a cliff, only to mistime her jump and tumbling her way down and landing face first on the beach. At the hotel, he awakens to her on top of him, sexually assaulting him in his sleep. She often becomes reckless and intoxicated and her behavior results in humiliation for Tim.Winstone takes the team for a shark tank dive off the coast with guide Komante (Rob Schneider), who has lost 3 fingers to shark bite. Missy forces her way onto the boat by jumping out, while Tim wanted the boat to leave without her. Once out in the ocean, she forces Tim to enter the cage with Winstone, even though Tim tried hard not to participate by saying he needed to take care of a sick Missy. Then Missy chops up some fish bits and throws them in the water to attract the sharks. A great white comes swimming and attacks the cage really hard. The cage breaks and the shark gets in. In the panic Tim breaks Winstone's nose. Komante punches the shark in the nose to make it go away. Missy administers CPR to Winstone to revive him after he swallows too much water in his lungs.Back at the room, TIm asks Missy to not venture out. Missy decides to spend time with Barbara (Arlene Newman) (staying in the room next door), who heard Tim & Missy have sex the night before. Barbara told her that her husband didn't make those noises since their honeymoon 30 yrs ago. Missy decides to go to a spa with Barbara. When Tim narrates this to Nate, he is horrified, since Barbara is Winstone's wife. TIm rushes back only to find that Missy had advised Barbara to break up with Winstone. Winstone finds out that Missy meddled in his marriage and in his rage he trips over and hurts his neck. Missy snaps his neck back into position and tells Winstone that he is responsible for the marriage falling apart.As time goes on, she starts to help Tim do well at his work retreat and also wins Winstone's favor towards Tim by hypnotizing him (she spent the whole night with Barbara and Winstone and used that opportunity to Hynotize him). At the talent show Tim's team puts in a really lousy performance but Winstone applauds Tim and keeps saying "I Love that guy". Tim asks Missy and she admits that she hypnotized him. Tim eventually begins to fall for her. Throughout Janice can see how much fun Missy is having and the laughs she shares with Tim. Janice reaches out to Missy, who convinces her to have a threesome with her and Tim Tim's workplace competitor, Jess (Jackie Sandler) ('The Barracuda'), is not pleased with Winstone giving a job to Tim instead of her. So Jess reveals to Missy that she was invited there by accident and wasn't the one Tim wanted to invite. Missy checks Tim's phone and finds out the truth. Saddened and devastated, she leaves Hawaii.Meanwhile, the actual Melissa arrives in Hawaii, having been invited by Jess. At lunch, Tim begins acting much like Missy did on their first date, taking multiple shots and performing a handstand in the diner. Tim lets her know that he has feelings for someone else and leaves Hawaii for Portland. Tim also removes the hypnotism Missy put on Winstone, and Tim ends up quitting his job. Tim meets with Missy and he apologizes and tells her all the things that he likes about her and that he wants to be more like her. She forgives him, and they kiss.