She shot upward, breaching the surface with a gasp. She was back in her room, tablet in hand. The screen displayed a single message:

The gates came faster. (x=6) – true. 4 = y + 1 (y=3) – true. Then a tricky one: x + x = x (x=0). 0+0=0. True. She almost missed it, but the eel’s eyes narrowed approvingly.

She opened the next level:

She was ready.

The screen shimmered, and suddenly Kaila wasn’t in her room anymore. She was standing on a rickety dock overlooking a bioluminescent sea. The air smelled of salt and rust. Beside her, a grizzled old diver named Gus was tightening the bolts on a brass diving helmet.