Katniss is disoriented when she enters the arena. Witnessing Cinna's assault has unhinged her. She gathers information about the arena - pink sky, white-hot sun, blue saltwater all around her. The Cornucopia sits on a circular island. Twelve spokes of land radiate from the island. Between each spoke two tributes wait on top of metal discs. Surrounding the water are concentric circles of thin beach and then dense greenery. When the gong sounds, Katniss swims towards the nearest spoke and races to the Cornucopia. As she grabs a golden bow, she realizes Finnick is behind her. He has a net and trident, his signature weapons that he wielded to victory in his own Games. Finnick teases Katniss and she assesses the situation. About to shoot an arrow at him, she sees a gold bangle patterned with flames on his wrist - the same one Haymitch wore in the Training Center. She takes this as a message from Haymitch to trust Finnick.
Finnick yells at Katniss to duck and he shoots the trident into the male victor from District 5, killing him. Katniss grabs more weapons - knives, an awl and another sheath of arrows - and deflects Enobaria with an arrow she dodges. Gloss isn't so lucky; he catches an arrow in the calf. Brutus uses his belt to protect himself from her arrows. Katniss finds Peeta stranded on his disc in the water. Finnick insists on retrieving him and is true to his word, for the moment dispelling Katniss's fears that he is untrustworthy.
Not wanting to leave her behind, Finnick scoops Mags out of the water. Katniss sees Beetee bobbing in the water and wants to suggest they wait for him too, but they have to move on. Katniss gives Mags the awl and Finnick hoists Mags onto his back. Katniss, Peeta, Finnick and Mags run into the greenery which turns out to be dense jungle. The jungle is humid and forbidding. Peeta takes the lead and cuts them a path in the vegetation. They take a rest after a mile and Katniss scales a tree to get a clear look at the Cornucopia. Several dead bodies litter the island. Whatever togetherness they found at the interview has dissolved quickly in the arena. Katniss figures she should just kill Finnick while she has the chance. But when she comes back down, Peeta puts himself between them and reminds them they should prioritize the search for water. At this point, Katniss knows they are better as a team.
The group keeps climbing up into the jungle, hopeful that there is a spring on the other side. Instead, Katniss sees a ripple in the sky - the same chink in the armor Wiress pointed out to her in the Training Center. Before she can warn Peeta, he stabs at vegetation with his knife and hits the force field. He is thrown backwards. Katniss sees his hair has been singed and his heart has stopped. Finnick performs CPR and revives Peeta, but Katniss can't help but sob uncontrollably. For the benefit of the audience, Finnick says it must be pregnancy hormones. Katniss is now indebted to Finnick for saving Peeta.
After a brief pause, they press on in search of water. Katniss lies and says she heard the force field, not wanting to reveal Wiress's shimmer clue. Instead, she shifts the blame on the Capitol doctors who repaired her hearing after losing it in her first Games. Katniss takes the lead, throwing nuts towards where she thinks the force field is. Mags eats them when they come back toasted. They make no progress to the left and Katniss realizes that the force field seems to herd them along a curved path. Katniss climbs a tree and sees the shape of the entire arena - perfect circle topped by a dome made of force field. She shoots an arrow towards the sky. After a flash of real blue sky, the arrow is thrown back to the jungle.
They reason there must be fresh water somewhere between the jungle and the island. They circle down, on the lookout for springs. By mid-afternoon, they need a break. They camp ten yards below the force field and begin to fry nuts. Katniss decides to go hunting, pausing to listen to the cannon blasts that signal eight tributes have been killed. She shoots a rodent and feels moisture on its muzzle; water must be somewhere. While she was gone, Mags and Finnick have created a hut out of grass mats. Katniss skins the rodent and Peeta skewers a cube of meat and hurls it into the force field. It fries too, and makes a good meal. Night falls and the anthem precedes the death count - a parade of images of the fallen: the man from District 5, male morphling from 6, Cecelia and Woof from 8, both from 9, the woman from 10 and Seeder from 11.
A silver parachute floats down to their shelter - a gift from one of their sponsors. It's a hollow metal tube with a lip on the end. Katniss realizes it is a spile, a spigot for tapping maple trees. Peeta burrows a hole into one of the trees and they hit water. Finnick takes the first watch and they try to get to rest. Twelve bells ring out, disrupting Katniss's sleep. No one knows what the sound means. A bolt electricity strikes a towering tree a distance away, triggering a lightning storm. When the lightning stops an hour later, rain picks up a few hundred yards away from their camp. It stops abruptly an hour later and a dense fog begins to roll. Tendrils of the fog reach out in an unnatural way and Katniss knows something is wrong with it. Her skin blisters where the mist hits her. She wakes the others and they run, with Mags on Finnick's back.
Peeta is slowed from his earlier injuries, but Katniss refuses to abandon him. All are affected by the fog, which is chemical in nature. In addition to the searing pain, it attacks their nerves. Half of Peeta's face droops and Katniss and Finnick have trouble controlling their limbs. Katniss and Finnick swap; Finnick hoists Peeta onto his back and Katniss carries Mags. However, Katniss struggles and falls. Mags rolls off her back. Finnick is overwhelmed; he can't carry both Peeta and Mags. Mags kisses Finnick and hobbles straight into the fog, sacrificing herself. Debilitated, the three of them fall into a pile, sure they will die too, but the fog is vacuumed up and disappears out of the arena. After the fog is gone, Peeta sees orange monkeys assemble in the trees.
Katniss, Peeta and Finnick crawl to the beach. Katniss sticks her hand in the water and the searing pain of the salt hitting her wounds abates after some time, leaching the poison out of her. She and Peeta submerge themselves to heal. They slowly introduce the water to Finnick until they can get his body into it inches at a time. They all start to feel better, but Finnick is upset about losing Mags. Peeta goes into the jungle for water while Finnick does some swimming tricks for Katniss. Eventually they go to join Peeta but Katniss sense a change - the monkeys are primed to attack. Katniss calls to Peeta without alarming him and the three form a triangle to defend themselves. Katniss shoots arrows, Finnick spears the monkeys with his trident, and Peeta slashes away with his knife. Peeta reaches for the sheath of arrows on his shoulders, leaving him temporarily exposed. Katniss dives towards him to protect him from a lunging monkey, but the morphling girl from District 6 gets there first. The monkey tears into her.
Alliances are cemented early on in the arena. Finnick and Mags join forces with Peeta and Katniss at the start of the Games. The District 4 victors are especially useful in an environment similar to that of their home – water. However, an initial bloodbath claims the lives of a third of the victors, undoing whatever sense of unity they had expressed the night before. Katniss is disappointed but also reasons that this reversion to survival mode means she should not trust anyone. She immediately begins to resent her bonding with Finnick. Finnick, however, makes himself indispensible.
Meanwhile, Finnick and the other tributes are all acting on behalf of the resistance. Katniss and Peeta have no idea that the rebels are planning on destroying the arena and breaking the victors out – the first act of war with the Capitol. To keep Katniss where they need her, Haymitch and the rebels have convinced the others to deceive her. They must keep Peeta alive in order to maintain a relationship with Katniss, who hasn't given up on her objective of ensuring Peeta’s safety.
Finnick revives Peeta when he runs into the forcefield and is electrocuted. Naturally, Katniss is suspicious of his motives but, in a rare show of emotions, weeps at Peeta’s side. Now she has one more person she owes, but she does not yet understand the true nature of the game. When the morphling from District 6 sacrifices herself to save Peeta in the monkey attack, Katniss knows something is up. Still, at this point, she has no choice but to work with the other tributes.
Mags has a moment of pure heroism when she sacrifices herself for Finnick, Katniss and Peeta. In later chapters, Katniss learns that Mags was Finnick’s mentor and the girl she volunteered for, Annie Cresta, is Finnick's love, a girl driven mad by the Games. Mags’s death is one of the first of many to come in both Catching Fire and Mockingjay that is motivated by self-sacrifice for the greater good.
Once again, the arena reveals the measure of Katniss’s intelligence and strength. Her discovery of the forcefield and identifying the use for the spile keeps her companions alive. She also intuits the deadly nature of the fog and recognizes that the monkeys are primed for attack. Katniss is a heroine who relies on all of her faculties, both mental and physical, to survive.