Sunset. Cumulus towering in the south, their tops spreading into anvils edged in a gold incandescence. Lightning trembled in the clouds, and the wind, yearned for in the morning, came on with the venom of an answered prayer. They sailed into the heart of a squall, main furled and foresail double-reefed, and when they sailed out of it, it was as though they had passed through a door from a tumultuous room into a serene one. The seas laid down, stars glittered like crystal rivets, and far behind the wake, the army of flickering clouds retreated to fading drum rolls of thunder.

Drew practiced with the sextant until he could take sights almost as fast as Will, and he eventually became quicker at the computations. He studied the constellations, observing how their positions changed as the latitude dropped. His faithful landmark, or skymark, was the summer triangle—Vega in Lyra, Deneb in the Northern Cross, and Altair in Aquila. On clear nights, his terror of open ocean diminished, and he felt himself one with the ancient mariners who had neither compass nor sextant nor even astrolabe but found their way by their knowledge of the skies.

The patent log’s torpedo swam in the wake, recording their speed and distance with such fidelity that they acquired an affection for the darting metal tube. It became a kind of mascot, and to honor its logging the miles of their exodus, they dubbed it “Little Israel.” When seaweed fouled it, they hauled it in, cleared it, and returned it to the water, giving it tender pats and instructing it to go back to work. Once, on Nathaniel and Eliot’s watch, a huge swordfish, mistaking the log for prey, swatted it with its bill to kill it; when it continued to swim, the swordfish charged, its entire body turning iridescent blue. For a moment, Little Israel’s life appeared to be over, but Double Eagle, brisking along at six knots, yanked it out of the swordfish’s mouth. A second later, the fish shot out of the water straight as a rocket, its blue flanks striped with lavender, shuddering and throwing off spray. At the top of its leap, it arced over and returned to the water headfirst. The two brothers looked at each other as if they had seen a hallucination. The creature had not looked like the swordfish in New England; its bill was shorter, its colors more vibrant. Drew had brought along an illustrated book of saltwater fishes, which they consulted, and identified the creature as makaira nigricans, a blue marlin. The book said blue marlin were habituated to semitropical waters, and Will speculated that the one Nathaniel and Eliot had seen had been following a tributary of the Gulf Stream, a theory supported by the color of the sea, a rich royal blue rather than green, and by the flying fish that could be seen skipping the surface like silver stones.