The two islands—the companions—came into sharper view. Theo was good at being alone, liked being alone, but he couldn’t imagine being trapped on a tiny island for twenty years with only doctors and nurses and birds for company.

“And that’s not the only tragedy,” said Aunt Esther. “In 1905, over one thousand people died when a steamship caught fire near the shore. They say that their ghosts haunt the island.”

Tess’s eyes went dark and wide as Underway tunnels. Aunt Esther laughed, her gray hair gleaming silver in the afternoon light.

“Oh, the ghosts aren’t scary. They’re just sad.”

“I’d be angry,” said Tess.

Aunt Esther regarded her. “Yes, I rather think you would.”

Tess blinked, because of the spray or because she didn’t know how to take Aunt Esther’s comment. But with North Brother Island getting closer and closer, Tess stopped asking questions. The island was lush and green with trees and bushes, with just a few smokestacks or towers peeking through the top of the nearly impenetrable canopy. Remnants of what must have been a dock stuck like wooden teeth from the water.

Aunt Esther slowly maneuvered the boat toward the shore, where some small part of the dock still looked intact.

“Are you going to let us off on the dock?” Theo said.

“What dock? Oh! That? That won’t bear your weight. We have to wreck ourselves on the beach. Well, not really. Mostly. A minor little shipwreck, that’s all.”

Tess tried to say something, but that something turned into a strangled yelp as Aunt Esther jammed the nose of the boat onto the scruffy sand. The boat bobbed and groaned in the water. Theo held on so that he wasn’t pitched over the side. It wasn’t deep, but something about the island was creeping him out already, and they hadn’t even begun their search.

“I’ll let you off here. You have”—Aunt Esther checked her wristwatch—“two hours to explore while I do a little fishing. Then, I expect you back at this very place. Don’t be late! If we get caught, we’ll be arrested!” She said this with gusto, as if she’d been waiting for the right opportunity to be arrested and this was it.

Theo, Tess, and Jamie carefully climbed out of the boat and onto the sand, sloshing water all over their sneakers. Theo grabbed the pack that Esther had given them, filled with snacks, water, bug spray, a compass, and a rudimentary map of the island she’d printed off the web.

“Thanks, Aunt Esther,” Theo said. “We really appreciate it.”

“Of course!” Aunt Esther said. “Take lots of pictures, don’t bother the nesting herons, don’t eat any berries, and don’t sit in any poison ivy. I did that once when I was doing field work for the museum. Awful. Give us a push, please!”