“We’re scared of dogs, okay?” said Chu. “Ond’s right, it’s time to go.”

The three of them focused on Chu’s Knot, trying to relax enough to enter the interbrane gap. But with all the worries, it was hard to get underway. Hard to get their heads in the right place. They took a break and talked a little more.

“Did you guys see a weird ocean when you came across?” Thuy asked Ond.

“That’s the Planck frontier,” said Ond. “Physics below the Planck length is a scale-inverted image of the physics above the Planck length. If someone were to shrink down below that foamy frontier, they’d feel like they were expanding into another cosmos. The world of the subdimensions.”

“The Hibraners call it Subdee,” said Chu. “And those bird-headed men are the subbies. Subbies from Subdee. Thanks to them it’s dangerous to jump branes.”

“They poke up their heads to eat our information,” said Ond.

“More than information,” said Chu. “They want to eat our bodies too.”

“I hate the subbies,” said Thuy.

A single ray of sun broke through the clouds to illuminate the little park.

“I want to jump back right now,” said Chu. “I want my orphidnet. Let’s ride the sunbeam. That’s how to do it. And remember to use my Knot to point you the right way. The subbies aren’t the only thing to worry about. You can get lost between the two branes. There’s a lot of different directions in hyperspace.”

Holding tight to the harp, Thuy wrapped the image of Chu’s Knot around the sunbeam—and then she was back in the interbrane teleportation zone, winging across that same endless sea, tracing its foam-flecked, wavy curves. Ond was next to her, helping her lug the harp, and beyond him was Chu, the three of them gliding along like superheroes.

Thuy was uneasy about the harp. The rushing wind kept setting its strings to vibrating. Repeatedly she reached out to damp them, but the magical instrument’s body was resonating with a low, persistent thrum—just the thing to attract unwanted attention.

And now, oh no, here came the subbies. At first they looked like fat, stubby plants, but Thuy felt a tingle, and once again she was seeing bird-headed beings with human bodies flying along beneath the surface. The beaked heads poked up and swiveled to stare at the harp. Four of them.

“Shoo!” screamed Chu, losing his cool. He veered into his father, nearly breaking Ond’s hold on the harp. A corner of the instrument dipped into the sea. The rushing surface set the transparent strings to singing a fresh chord, mellower than the ones before. Rainbows of quantum foam kicked up.

Squawking and gabbling, the subbies tugged at the harp with their cartoony white-gloved hands.