AFTER WE’VE MADE out, and then eaten lunch, and then made out some more, I realize that I still need to get to the diamonds. It’s midafternoon, and we should probably head back soon. I can’t put it off any longer.

“I’m going to take that dip now,” I say.

“Maybe I’ll go with you,” she says.

I’m worried for a moment, but I don’t think she’ll actually go through with it. The lake is pure snowmelt. Even in the warmest summer months, the water probably never gets above seventy degrees.

Claire kicks off her shoes, and we wade out into the water together. Cold engulfs my feet, and pain crawls up my legs, as if the chill is a living thing creeping through my bloodstream.

Claire inhales sharply and makes it as far as her knees, and then she splashes out of the water and back up onto the bank.

“No way,” she says, hopping up and down. “That’s impossible.”

Her legs are red up to her knees, as if she stepped into boiling hot water instead of cold.

“You’re crazy,” she adds.

“I’m just more acclimated than you are,” I say.

With that, I turn and dive forward under the water. I swim for about twenty yards and come to a rock island about the size of a Volkswagen Beetle. I climb up on top to rest, but the air against my skin is even colder than the water. I wave at Claire and then dive off the other side.

The lake is as clear as drinking water. Sunbeams shine down through the water as I swim over and around boulders.

I bypass a couple small islands and finally arrive at an island a hundred yards from shore. It’s rounded and about the size of a small backyard, rising up like the back of a white whale. I recognize it because of one gnarled tree that’s growing out of the rock like the twisted, arthritic hand of a skeleton, beckoning me to my buried treasure.

The stone bank angles into the water, and I crawl up on the rock and lie on my back. My chest heaves. My body feels like it’s glowing. After a minute, I rise, my limbs trembling. I wave at Claire, who is sitting on the bank.

I walk across the island, my wet feet slapping the granite. I find the crack I recognize, a point where two slabs of rock come together, and follow it to the edge of the water. There is a sheer drop-off on this side of the island.

I take a deep breath and dive straight down. The water is colder the deeper I get, like ice packed around my body. I keep my eyes open, and the cold seeps into my sockets. My ears ache from the depth.