He leans back in the seat, staring at the dashboard. “During the last ice age, water levels dropped, and the cave systems were no longer flooded. This allowed tremendous stalactites, stalagmites, and other calcium carbonate formations to form within the karst.”

“Karst?”

“Karst is the scientific name for a porous, limestone geology. The Yucatan is all karst. Anyway, about fourteen thousand years ago, the ice melted and the sea rose, reflooding the caves. There are no surface rivers in the Yucatan. All the peninsula’s water supplies originate from the subterranean caverns. The inland wells are freshwater, but as you near the coast, they become more salty. Sometimes the ceiling of a cave would collapse, forming a giant sinkhole—”

“Like the sacred dzonot?”

Mick smiles. “You used the Mayan word for cenote, I was wondering if you even knew it.”

“My grandmother was Mayan. She told me the dzonots were believed to be portals into the Underworld—into Xibalba. Mick, you and your mother—the two of you were very close, weren’t you?”

“Until recently, she was my only friend.”

Dominique swallows the lump in her throat. “When we were in the Gulf, you started to tell me something about how she died. You seemed angry at your father.”

A look of uncertainty crosses his face. “We really should get going—”

“No, wait—tell me what happened. Maybe I can help. If you can’t trust me, whom can you trust?”

He leans forward, his forearms on the wheel as he gazes out the bug-encrusted windshield. “I was twelve. We were living in this two-room shack just outside Nazca. My mother was dying, the cancer having spread beyond her pancreas. She couldn’t handle any more radiation or chemotherapy, and she was too weak to care for herself. Julius couldn’t afford a nurse, so he left me in charge while he continued his work in the desert. Mom’s organs were failing. She’d lie in bed, curled in a ball against the abdominal pain, while I’d brush her hair and read to her. She had long, dark hair, just like you. In the end, I couldn’t even brush it, it was just coming out in clumps.”

A single tear rolls down his cheek. “Her mind stayed sharp though, even up to the very end. She was always strongest in the morning, able to carry on conversations, but by late afternoon, she’d become weak and incoherent, the morphine knocking the fight right out of her. One evening Julius came home, exhausted after having spent three straight days in the desert. Mom had had a bad day. She was fighting a high fever and was in a lot of pain, and I was wiped out from having cared for her over the past seventy-two hours. Julius sat on the edge of her bed and just stared at her. Finally, I said good night and shut the adjoining door to their bedroom to get some sleep.