From Will Ludwigsen, the sequel to his Shirley Jackson Award finalist A Scout is Brave:

In 1963, thirteen-year-old Bud Castillo helped his family thwart a conspiracy to unleash ancient horrors from beneath Devil's Reef—and met Aubrey Marsh, a boy unlike any other, whose watery fate Bud has never quite stopped mourning. He's spent the years since trying to put Innsmouth behind him. Now serving in the chaos of the Mekong Delta five years later, Bud finds that piloting a Swift Boat through a war nobody wants to win feels uncomfortably familiar: a battle of deranged true believers trying to get their hands on something ancient and hungry. This time, though, the conspiracy runs from the jungle rivers all the way into the American intelligence community—and Bud will need more than a Scout's sense of duty to survive it. Especially when a ghost from Innsmouth surfaces to remind him that loyalty is the most dangerous virtue a man can carry into a war.
 
Funny, furious, and shot through with genuine heart, A Scout Is Loyal is a Lovecraftian war novel about doing the right thing not because the handbook says so, but because some ideals—and people—are worth our loyalty.