Mahiri Barrage feels the most comfortable on the water. When she's not working at her family's boat repair and rental business, she can be found rowing or fishing on the great Byness River. When Mahiri's mother, the discharged Captain Amoreena Barrage, receives a summons to return to the Queen's Navy as a lighthouse sentry, Mahiri knows something isn't right. Weeks go by with no word from Amoreena to the Barrages in their little village of Whencewend. When Mahiri's father refuses to let Mahiri investigate what's happening on the coast, Mahiri takes matters into her own hands. Accompanied by her cat, Dustbunny, Mahiri sets off to find out what's happening on the secret mission at the light station.
In Port Wyndron, ships are disappearing. Rowing shells, trading vessels, and other boats traveling Wyndron Sound have vanished without word from captain or crew. Mahiri wonders if this is related to her mother's strange assignment. Her journey begins as she heads down to the bustling port city to find out.