Ginnie, Lettie, and the boy walk to the place where the opal miner parked the Mini to die. Gran is still sleeping and won't wake up until she's ready—it could be minutes, or a hundred years. (Sounds dreamy, right?)
The varmints arrive, and they're ravenous—they want to eat the doorway in the boy's heart, and they're definitely not leaving until they get what they came for.
The boy is protected because he's on the Hempstock's land, but the hunger birds are not having it, so they start eating the world that borders their farm. They eat the trees and the roads and everything, leaving just a gray void.
Just when Lettie has convinced Ginnie they need to wake up Gran, the boy runs toward the varmints to stop the potential destruction of the world by sacrificing himself.
He gets tackled to the ground by Lettie, who calls him an idiot and holds him face down in the grass.
The hunger birds go after Lettie instead; he can hear her screaming in pain.
Gran appears—glowing brightly—and stops the birds with a firm voice, demanding they cease. They have broken laws, treaties, and pacts by harming Lettie, and Ginnie takes her body and his and holds them to her as she weeps.
Gran starts threatening the hunger birds with awful consequences for their actions, but insists that she'll deal with them later after she's tended to her children. She makes them put everything back the way they found it. (Now there's a perfect example of a stern granny-scolding.)
Lettie is not okay. She's not dead, because her kind doesn't die, exactly, but she's hurt as badly as she can be.
Ginnie carries Lettie's body into the ocean and releases it into the waters. Gran tells the boy not to be sorry because she's not dead—she's been given to her ocean, and one day when it's ready, the ocean will give her back.
Lettie's body is consumed by a giant wave (the ocean has now expanded as far as the boy can see) and the water goes calm.