Nancy and Bess head off to Halloway College for winter break to investigate the disappearance of a girl named Ava Woods. Now, it's not like they actually know each other or anything, but Carson Drew apparently knows her parents and suggested his daughter could find out what happened. She disappeared after meeting a blind date on Friday night, and the girls arrive on Sunday to meet with the dean.
The dean lets them know that they are in luck. Even though it's winter break, the school offers a special elective program that is open to students and people from off-campus that lets them take a class on campus. As the school obviously has a lack of money, there are even dorm rooms open for those new students! Nancy heads off to the dorm, while Bess signs them up for classes.
She quickly meets Ava's roommate Betsy, who has no clue what happened to her. She does remember that someone called for Ava and mumbled something about a box before hanging up. Nancy also meets Darien, some random super cocky guy who hits her with a snowball and then hits on her. She hits up Campus Connections, which is an absolutely adorable “computer dating” service open to students. Luke, the owner and founder, claims he doesn't remember anything about Ava or her date.
The following day, Nancy sees a suspicious woman going through Ava's desk. The woman introduces herself as Maia, Ava's boss, and claims she was worried when Ava never showed up and wanted to leave her a message. Maia and her fiance run an elderly support company. Nancy gets just enough information to call Ava's client and learns the woman has no idea where Ava is and that she didn't call about a box.
Nancy winds up in an astronomy class, which was one of the only classes left. Darien and Luke are both in the class too, and while Darien lures at her like some creeper, Luke glares at her. She also learns that Ava randomly took off the year before and came back with big stories about heading off on spring break. Nancy also finds out that Ava had a serious relationship with Vincent, the star of the hockey team and a major hot head, so she encourages Bess to fill out a dating profile and try to get the hook up with the hockey team.
The two girls head back to the dorms after their classes and hear the phone ringing in Ava's room. Nancy uses her awesome B&E skills to pick the lock and get to the phone, but all she hears is some older lady talking about a box again. This somehow convinces her to sneak over to Luke's room and break in while he's gone. She discovers that Bess has a date set up with Vincent and that all of Ava's files are gone. While trying to get out, she accidentally trips over something and realizes it's Luke's body just as someone hits her over the head and knocks her out. Does she ever not get knocked out? Girl should wear a helmet on jobs.
The cops instantly think she did it and keep hounding her, despite the fact that they found her knocked out and can't locate the gun. They finally let her go but tell her she's now officially off the case. While heading back to the dorm, Darien conveniently comes by and offers her a ride back. He acts creepy again, and she gets out of the car fast.
Mr. and Mrs. Woods show up the next day and tell her to leave the investigation to the police, but when she says she wants to continue, Mrs. Woods lets her. She managed to find out that Ava's date was with someone named Jim and got her hands on all the guys named Jim who used the dating service. After visiting a few guys, she finds out that all were already visited by a “reporter” who she finds out was Darien. She also discovers that he writes for the paper and published a big story that day, which shows her being led into a police car.
Nancy also takes a trip to see Vincent. Even though he's super hot, he blows her off, acts really rude, and ditches her. Though she tries to get a job where Ava worked, they turn her down and say there aren't any jobs available. When Bess goes, she gets a job on the spot. The two then get ready for the night. Bess has her date with Vincent, and Nancy wants to spy on them.
Vincent shows up in a sweatsuit and looks really unhappy. He says he has to skip their date and that he tried to call and tell her. Bess uses all her charms to get him to stay and eat with her. He finally tells her that his ex-girlfriend went missing and that he can't concentrate. It must not hurt him too much because by the end of the night, he's smiling, laughing, and telling her how he's glad he came. That is until he sees Nancy and storms across the room, accusing her of murdering Ava. Man, I hope this chick is in Florida.
Bess gets him called down to the point where he agrees to help them. Even though she kind of likes him, she realizes he's still in love with Ava, so she moves onto the next guy on her list the next day. Nancy goes to the newspaper office to find Darien and finds him with Betsy, his girlfriend, in his arms. Betsy confesses that she was helping him investigate Ava's disappearance to help him get a job on a real paper but told him to stop when Nancy showed up. He very obviously did not stop.
Betsy remembers that Ava had a secret locker, but it has a combination lock that Nancy can't pick. They call Vincent, he acts weird around Betsy, opens the locker, and runs away. All they really find is proof that she had a safety deposit box at the bank. Betsy later has Nancy come in and listen to a message someone left for Ava about the switch being different. Oh, and then someone breaks into Nancy's room without taking anything.
Bess suddenly shows up with her date of the day, Jim. Jim says he had a date scheduled with Ava for Friday night but that Luke called at the last minute and canceled it. Nancy decides that she should check out Luke's place and gets Darien to help. They break into his mailbox and find his bank statement, which shows that he deposited $500 on the same day Ava went missing. Before they can do anything else, someone catches them, which is bad because it's after hours and it's an all guys dorm, so Darien starts making out with her. Nice guy.
She and Darien go to meet with the dean, and since the school doesn't follow banking laws, he makes one call and gets Nancy into the bank. The head of the bank pulls up Luke's files and gives her all the information she wants. Luke deposited $500 on Friday and came in the next day to empty his account. He also made the deposit in cash and apparently only made tiny deposits in the past.
Nancy goes to visit Bess at work and gets to hear all about Peter, Maia's fiance. Every girl who works there has a crush on him and thinks he's just the best. She also finds a key that Ava hid away and a random address. When she goes to the address, she finds Maia in a fancy ballgown and expensive jewelry. Maia gives her a tour of the enormous and expensive house and says they rented it from one of Peter's college friends. She also poo poohs the idea that Peter is an artist, even though Nancy heard it from others.
When she gets back to the dorm, Bess calls with big news. Her client just asked her to make a deposit for her at the bank. Nancy runs down with the key and learns it wasn't from that bank. They find out that all the employees of the company have access to the boxes and that Peter does too. In fact, he often stops by to make deposits. Not suspicious at all. Bess drops off her client's things while they gossip about whether Peter is behind Ava's disappearance.
They somehow figure out what bank Ava used and sneak over. Nancy dons a fake hat to look more like Ava, and Bess has her put a Popsicle stick in her glove to make it look like she broke her finger. The banker really doesn't give a shit and gives her access to the box. There, she finds a bunch of expensive jewelry in a fancy box with one piece missing. This somehow makes her realize that Peter and Maia have been stealing from their clients.
After pocketing the box, she asks the banker if she can rent another box and tells him the jewelry box wouldn't fit in her old box. She also fakes being in pain so she can't fill out the paperwork with Ava's information and asks him to keep both keys for her after putting the jewelry in the new box. She and Bess sneak over to Peter's house, break into his garage, and find that he has a ton of dental plaster on hand. Turns out that he's been using it to make molds of their clients' keys so they can steal from them.
The fancy house conveniently has its own fishing cottage, which is where they figure the couple hid Ava. While sneaking out there, Peter shows up, grabs Bess, and threatens her with a gun. Maia shows up and helps him tie the girls up with Ava. There's a bunch of exposition on how they stole from their clients, Maia grew up poor, and she got tired of it. Peter waves his gun around some more until Nancy tricks him into going after the last few pieces. He takes Ava with him to sneak her in and leaves Maia to watch over Nancy and Bess.
Nancy waits until he's gone to fake having a seizure. She literally smacks the gun out of Maia's hand, and then, even though Nancy hates guns, she holds it on the other woman and threatens to shoot her if she moves. When Peter comes back, Nancy hits the door so hard that it smacks into his head. While she and Bess take off running, he goes after Ava. They wind up fighting in the middle of the frozen lake where the cottage sits before crashing through the ice. Suddenly, the cops show up, save Ava, and arrest Peter.
Cut to the whole gang sitting around a fireplace and roasting marshmallows. Ava tells them how she discovered the thefts and how Maia was the one who started. Vincent shows up to profess his love for Ava, and she tells him she loves him too. Mrs. Woods says that the school decided to take over the elder care business as long as Ava agrees to run it. Nancy laughingly suggests Bess sign up, and Bess points out that she's terrible at taking care of old people but great at dating!