The book opens with a nice surprise: "Uncle" Victor Briggs, a family friend, has planned an impromptu weekend for Sym Wates and her mother in France. Sym is thrilled. So thrilled, in fact, that she's able to overlook the fact that Victor steals her mother's passport, thus leaving her behind in England. In Paris, sans Sym's mother, Victor reveals a second surprise: Their final destination is actually the South Pole. As in Antarctica.
Now, there are a lot of things the average person might feel if her weekend jaunt to Paris turned into an epic Antarctic adventure. Alarmed, for instance, or perhaps disappointed. Not Sym, though—she just feels delighted. She's eager to put some distance between herself and her real life, which hasn't been so good lately. Sym doesn't have many friends, for one thing, and for another, her father recently died from a grisly illness. It's time to chill. Literally.
At the South Pole, Sym and Victor set up base camp with a travel outfit called Pengwings. There, they join forces with a pair of con men, Manfred and Sigurd Bruch, who are posing as a Viking filmmaker and his son. Oh goodie.
Unbeknownst to everyone, Victor blows up a plane and drugs almost everyone at camp so the four can steal off in the night. Victor's secret agenda is to find Symmes's Hole, an imaginary portal to the center of earth that he's been obsessed with for years. Manfred and Sigurd's secret agenda is to steal Victor's money. Sym's secret agenda is keeping everyone else's secret agenda a secret from herself. Through her conversations with Titus Oates—her 125-year-old imaginary boyfriend and alter ego (who, incidentally, died on an expedition in Antarctica), we know that she's observant and suspects things are not as they seem. She willfully ignores these misgivings, though, to Titus's chagrin.
After a harrowing car ride across thin ice, Manfred admits to his con. Victor, who is fully cracked, just murders him and keeps on truckin'. For Sym, the expedition goes from bad to worse when Victor admits to a series of betrayals (including murdering Sym's father and swindling her family out of a lot of money) and sends her and Sigurd out in front of the vehicle to scout for cracks in the ice. It's nerve-wracking work, to say the least, but not nearly so nerve-wracking as when Sigurd manages to steal the vehicle, leaving Sym and Victor for dead in the snow.
Soon after all that, good old Uncle Victor throws himself down into the abyss he takes to be Symmes's Hole. Whoa.
Sym's learned a lot of difficult truths about Victor just before she watches him plunge to his death, and at first she's unable to deal. Overwhelmed by her feelings, she wants nothing so much as to lie down in the snow and die. Fortunately, Titus manages to talk her out of this terrible plan and helps lead her to safety, or at least some approximation of it: Sigurd, whose vehicle has stalled out in the snow. Sigurd takes Sym in, shoots her up with some adrenaline from the first aid kit, and she comes back to life.
From there, everything's pretty much easy street. In the hopes they'll be spotted by rescuers, Sym blows up the broken-down vehicle. No one sees it, but they're rescued anyway. On the long boat ride home, as she recovers from her arduous journey, Sym learns she has an admirer: Mike, one of her fellow travelers from the Pengwings tour. Much to her surprise, he asks her out. She's not ready to date yet—she's only fourteen—but she knows she will be someday soon.