He’s brought along boxes of handcrafted Jules Verne ray guns so we can run around the boat all weekend pretending to shoot one another while yelling Pew-pew! I’m starting to doubt his sanity. And I’m starting to doubt my sanity for following his orders.

“Sir.” I struggle to keep the anger out of my voice. “Maybe you can tell us what’s going on. Then we can play with your toys later?”

I expect him to yell at me. I’m prepared for that. I really don’t care anymore. Instead, he studies me with a sad, heavy expression—the kind I got from HP faculty whenever they mentioned my parents.

“Prefect Twain, may I?” Hewett holds out his hand.

Reluctantly, Gem surrenders the Leyden gun.

Dr. Hewett looks it over, maybe checking the settings. He gives Gem a weary smile. “I hope you’ll forgive me, Prefect. This will be faster than explaining.”

“Sir?” Gem asks.

Hewett shoots him. The only sound is a high-pressure hiss. For a millisecond, Gem is wrapped in flickering white tendrils of electricity.

Then his eyes cross, and he collapses in a heap.

“You killed him!” Franklin rushes to Gem’s side.

Hewett turns a dial on the stock of his weapon and nonchalantly says, “Did I?”

Tia looks at me with alarm, silently asking what we should do.

I’m paralyzed between the desire to help Gem and the urge to tackle our teacher.

Franklin presses two fingers against Gem’s neck. “N-no. He’s got a strong pulse.” He scowls at Dr. Hewett. “You can’t just go around electrocuting people!”

“There will be no permanent damage,” Hewett assures us.

“That’s kind of not the point,” I say, at the risk of getting shot.

Having heard that Gem won’t die, Tia turns her attention to her own Leyden gun. Like any good Cephalopod, she sets it down and starts to disassemble it. Her mass of bronze corkscrew hair sways and bounces around her face like the coils of a complicated machine. She extracts a projectile from the top of the magazine and holds it up for inspection. It’s a shiny white lozenge about the size and shape of…Well, honestly, the first thing it reminds me of is a tampon.

“Some kind of glass?” Tia asks.

“Not exactly,” says Hewett. “Each projectile is based on a Leyden jar. It stores an electrical charge that is released upon impact. But the casing is constructed from a special type of secreted calcium carbonate.”

“Like abalone shell,” I say.

Hewett looks pleased. “Precisely, Prefect Dakkar.”

I try not to feel gratified about giving him a correct response. We’re not in class anymore. Also, he just shot my bodyguard.

“If the casing is secreted,” I say, “what is it secreted from?”

Hewett just smiles. Suddenly I don’t want to know.

“Upon discharge,” he says, “every trace of the projectile is destroyed. The stun effect lasts anywhere from a few minutes to an hour, depending on the target’s constitution.”