“Forty means we’re not bringing them up,” Kai said, his voice flat. “We’re carving them out.”

She had. In her personal copy of the manual, next to the final step of the Chimney Protocol, she had written in red ink: “The only vertical that matters is the will to go back down.”

CODE VERTICAL-40. SOLO CAVER, 80M DEEP. CHIMNEY COLLAPSE. SECONDARY SEISMIC EXPECTED.

Thorne was conscious. He looked up at the stars, then at Lena. His lips moved.

“Three.”