Surface Interval

"Everybody comes home," Marcus Bell tells the Bayou City Divers before their trip of a lifetime. "That's the only rule."

Twelve days aboard the Aziza on the remote reefs of Sudan's Red Sea: hammerheads at dawn, a sunken World War II bomb ship, and coral gardens few people have ever seen. For Jonathan and Maggie Henderson, married thirty-three years, it is a chance to leave Houston—and everyone who might need them—far behind.

Then the engines fail in the desolate south. On a perfect morning, a...