Cara and Mark are throwing a last minute party when she takes the time to think about things. Their young, very young as she keeps saying, parents are computer specialists who always accept jobs in new cities and then join a bunch of clubs to meet new people instead of spending time with their kids. They had a fight that morning because they thought Mark spent too much time with his new girlfriend Gena.
A random cop shows up on the doorstep in an unmarked car. He acts a little shifty when asking about her parents and says there was a robbery a few houses down. After giving her his card and asking her to call anytime, he gets in his car which barely makes a sound, and leaves. Cara figures that's the perfect time to end the party.
Both think it's weird that their parents aren't home and didn't call until they find that the phone is out. They then a hear footsteps upstairs and freak out until their cousin Rogers walks out. Turns out that he moved in and that they keep forgetting he's there. That must be hard on his ego. Cara goes upstairs and flips out because their parents bed is unmade and they always make it, while Mark is just disappointed that he didn't ask Gena to stay longer.
Roger shows up long enough to scare them again with a black box in his hands. He claims it's his Walkman and that he forgot his headphones before shoving it in his pocket and running back to his room in the attic. Right before they leave, Cara finds something on the bed. It's a little tiny skull made from ivory. She thinks it's weird because it feels cold in her hand, but Mark just laughs it off.
Mark wakes up in the middle of the night, stubs his toe, and sees the little skull staring at him, but he can't remember taking it in his room. Later, he looks outside and sees a black van on the street, which he saw earlier in the night. He then sees Roger climb inside. After falling asleep and waking up again, he sees the van still there and the skull in a new spot.
The next morning, he tells Cara what he saw. Since Roger left for the day, they sneak up to his room and go through his stuff. They wind up finding a loaded gun hidden in a drawer, and Cara finds that he hasn't used any of his books and never wrote any notes despite supposedly being a college student. Cara then goes to their neighbor's house. The woman is a smoker, which we never see in YA books anymore, and asks a bunch of probing questions about her parents before saying that the place where they work has a lot of government contracts. Cara calls the phone company to come out and check her line, and when she gets home, she finds her parents' car, which they use to get to work, in the garage.
Cara and Mark skip school to see where their parents work and to get some help. They see the same van sitting outside, but the guy driving it says that he doesn't know a Roger. Mark doesn't believe him for some reason. They get to the place where their parents work and meet a bunch of people who never heard of them before. The CEO even comes down and tells them that no one by those names work there or ever had worked there.
Mark stops to call Gena and talk to her, but she acts really weird. When Cara gets home, she finds Mark sitting in the dark. He says that Gena dumped him and that she said she had to break up with him. He went over to her house to talk to her, but her dad answered the door and said she was so upset over something that she had to stay home from school all day. Nice dad to let her stay home for no reason. Cara then calls the cop from the other night and he agrees to investigate her parent's disappearance. When she hangs up though, she realizes that Roger was listening in on an upstairs extension.
When Roger comes downstairs, Cara accuses him of spying on them. After she brings up him being suspicious and the gun he has, he accuses her of spying and says that the gun belonged to his dad, who was a cop. He died a few days after giving it to them. He also claims that he too saw the van but never ever got inside it.
Cara doesn't believe him, and when he leaves, she decides to follow him. Mark stays home and gets a call from Gena. She cries and tries to tell him something, but when he presses her, the phone disconnects. Since he's a hormonal teen, he goes right to her house and cuts through the Fear Street woods. Something starts following him, which turns out to be an enormous dog.
Mark manages to break its neck before realizing that the dog was specifically trained to sneak up on people without making a noise. The dog also had a collar with a skull on it that looks just like the one they found in their parents' room. He then gets to Gena's house, climbs up a trellis to her window, and slips and falls.
This is one of those annoying books that bounces back and forth between two different characters using first-person, so we go back to Cara. After tracking Roger to a coffee house, she sees him sit down inside with the guy from the van. Roger sees her, accuses her of spying again, and then introduces him as his college adviser. Cara makes up an excuse to leave, sees them talking all secretive, and then starts heading home, only to find someone following her.
Turns out that it's Captain Farrday, the cop from before. He tells her that he hasn't found out anything new about her parents but that they'll show up. She then tells him all about her weird cousin, and he agrees to look into both him and the professor. As an added bonus, when she brings up the skull charm, he asks if he can see it. Luckily for her, probably, she can't find it. Right after he leaves, she hears another car pull up. It's only a friend from school though.
Mark manages to keep himself from falling off the trellis and gets into Gena's room. It looks completely clean and like no one had been there all day. There's a noise in the hall and her dad rushes in with a gun in his hand. He calms down when he sees that it's just Mark. Gena's dad tells him that she was so upset over their breakup that she took off to stay with her cousin, but Mark notices that she left behind her book bag.
Cut to the next day or a few days later, with the two talking about everything that happened lately. Cara suddenly remembers Wally, a friend of their parents who works with them. They look him up in the phonebook and head to his house. Through Wally, they find their parents listed in the work directory, call, and get their voicemail, so they know their parents really do work there. When they get home, they find Roger dead in his room as Captain Farraday bursts through the door.
Farraday accuses Mark of killing his cousin and marches them downstairs. The guy from the van bursts in, Cara shouts out who he is, and Farraday shoots him three times point blank. He then grabs the phone and calls the police station to report it. Since Mark just saw two dead bodies, he really needs a drink of water. When he heads into the kitchen though, he finds out that the phone is dead again and that Farraday called no one.
He keeps trying to find a way to warn his sister and then just snaps and calls out the other man. Farrday knocks him down and waves his gun around while shouting about how he was a cop until their parents did something and how he hates them. Before he can do anything, Gena rushes in with a hunting rifle. She keeps threatening Farraday and fires a shot at the wall behind him. They lock him in the garage, and she runs into the woods, telling them to follow her as she babbles about having to get there before the meeting starts.
Turns out that her dad belongs to some weird cult named the Brotherhood and the CEO of the company is the leader. They all put on robes and sneak into the meeting, where they see their parents in the center. Though they think their parents are the leaders, the group actually plans to kill them. Mark distracts them, which lets his dad jump up and reveal himself as a member of the FBI. After arresting a few people, they take their kids home and explain what happened.
They are apparently top secret FBI agents bringing down subservient groups, which is why they move all the time, and both Roger and the professor were agents. Farraday was a cop they busted in the past who came back for revenge. As an odd footnote, there's literally no mention of what happened to him after they locked him in the garage. They come home, drink cocoa, and talk.
Their dad tells them that all their covers are blown now and they have to move. Gena stops by to tell Mark that she's moving to Detroit to live with her mom while her dad is in jail. They kiss goodbye, Mark says he'll call, and she gives him a gift before leaving. It's a copy of the skull with a note inside that says she loves him and has her phone number and address in Detroit. Ah, it's a classic story of teenage love mattering more than the federal government.