Gus could feel his heart trying to pound its way out of his chest, as if it was hoping to get to the top of the stairs even if it meant leaving the rest of him behind. He needed to get up there. He needed to find Professor Kitteredge and find out what was wrong. But there was no way he was going to get through this crowd, not before the statute of limitations on whatever crime had taken place up above had run out.

He was about to give up and search for a side entrance when the people around him began to move aside. Before he could figure out what was going on, Gus heard a voice coming from the bottom of the stairs.

“No need to worry-it’s not contagious,” said the voice, which Gus quickly realized belonged to Shawn. “Not unless you get within thirty feet of the victim, that is. And even then, it’s so quick you’ll never know what hit you.”

Gus turned and saw the crowd parting as if it had been Charlton Heston coming up the steps. It was Shawn, his mouth and nose covered by a surgical mask. “No need to move away from me; I’ve been around this plague all day, and I don’t feel a thing.”

“What are you doing?” Gus whispered as Shawn stepped up beside him.

“Clearing a path,” Shawn said.

“Where did you get the mask?”

“Amazing what you can find in the average police car,” Shawn said. “The shotgun probably would have worked even faster, but they’ve got those things locked down tight. Let’s go.”

Shawn headed up the stairs, and as the crowd oozed out of his way Gus followed. It took only seconds to get to the top, where Shawn whipped off his mask. And then froze.

“Oh my God,” Shawn said. “No wonder everyone ran out of the museum.”

“What is?” Gus said, pushing his way to Shawn’s side.

“It must have escaped from the zoo,” Shawn said.