When Katniss wakes up that morning, she feels very happy, and she knows that feeling is connected to Peeta. She acknowledges that, given her current circumstances, it is crazy to feel happiness, but she revels in it before she has to fully wake up and face the reality of the Games.
They receive another parachute of rolls from District 3 and have some breakfast while Katniss ponders the others' actions. She is confused about why the others seem to be protecting Peeta. She considers that they might be doing so for purely selfish reasons. She decides that if they aren't protecting him, then they are just gaining Katniss and Peeta's trust to lure them into a trap. Either way, Katniss doesn't know what is going on, so she decides it's time for her and Peeta to break away from the others.
On the pretense of teaching Peeta how to swim, she takes him to the water to tell him it is time for them to split from the others. He agrees to do so but says they should wait until the two remaining Careers, Brutus and Enobaria, are killed. According to Peeta, Beetee is setting up a trap to kill them now. Though she is hesitant to wait that long, Katniss agrees.
Afterward, they return to the beach to listen to Beetee's plan on how to kill Brutus and Enobaria. Beetee points out that at noon and midnight, a lightning bolt hits the tree at the edge of the jungle, close to the force field. After it hits at noon, he wants to run his coiled wire all the way from the lightning tree down to the water. When the next bolt strikes at midnight, it will theoretically electrocute anyone in the water, or on the beach. He believes Brutus and Enobaria will be in either of those places at midnight, and that they will die.
No one disagrees with Beetee's plan, so the group leaves their camp on the beach to head to the lightning tree. They see the lightning strike at noon and spend the rest of the day napping while Beetee works with his wire. At dinner, the group enjoys a large feast of shellfish and oysters. When Peeta opens one of the oysters, he finds a tiny pearl inside. He gives it to Katniss as a gift.
She accepts the gift, noting that it is the last gift she can accept from Peeta. She cannot let him give up his life for her, so this will be the final gift she will enjoy from Peeta. Peeta, sensing her realization of this, says that giving her the locket the night before worked, but not in the way he needed it to.
This chapter continues the motif of relationships and the theme of imprisonment. Though Katniss wants to be able to enjoy her developing love for Peeta, she knows her current situation prevents that from ever happening. She isn't sure why she feels so happy, and this is another example of the Capitol trapping Katniss in a world where she cannot control or act upon her feelings. Instead, she must push them aside and lock them away.
The theme of trust is also explored in this chapter when Katniss decides she and Peeta can no longer work with the others. She determines that even if they are trying to save Peeta, she can't trust them anymore because it only makes her and Peeta easier prey. It seems Katniss' fear of trusting others has overcome the number of times she's witnessed Finnick, Beetee, and Johanna work to save Peeta and help Katniss.
The tree and the wire become more examples of using a Capitol invention in way other than the Capitol intended, another symbol of rebellion — like the force field, Haymitch's victory in his Games, and the poisonous berries from Katniss and Peeta's Games. Katniss and the others aren't sure if Beetee's plan will work, but if it does, there is reason to believe the Capitol will not approve. The lightning tree and Beetee's wire have become symbols of rebellion because they're being used as a weapon to defeat the Careers, which are beloved by and praised throughout the Capitol for their love of the Games.
Using an invention of the Gamemakers to kill the Careers would not only insult Snow and the Capitol but also give Katniss and Peeta a better chance of surviving. But it could possibly inspire rebels to also use Capitol creations to overcome Snow. The Capitol, struggling to end the rebellions, cannot afford to be made a mockery of again by Katniss or other tributes.
Peeta's realization that his locket failed to convince Katniss to let him die for her greatly upsets him. The pearl represents their final gifts to each other. Peeta's final gift to Katniss is the only beautiful thing about the arena. Katniss' accepting the pearl is a gift to him because, as she notes, it is the last thing she can accept from him.
From here on out, every action Peeta takes is an attempt to save her. Knowing this, Katniss realizes she will not be able to accept anything else Peeta offers her. She must let herself die and keep him alive so she can give himself, Panem, and future generations the possibility of a future without the Capitol and the Games. Her trust in Peeta's good nature and speaking abilities and the rebel cause is strong enough for her to sacrifice her life, even though she knows it will break her family's, Gale's, and Peeta's hearts.