I think Theo had watched me for a while before he came out there, waiting for me to pull myself together. My cheeks were flushed and tear streaked. I’d blown my nose so many times that it felt raw every time I inhaled. My head throbbed. But for the moment, I’d cried myself out.

Theo sat on the steps beside me, jittery, on edge, one foot bouncing up and down. “Listen,” he said. “I’m about to do something stupid.”

“What?”

His dark eyes met mine, so intent that I thought, for one crazy moment, despite everything that was going on, he was about to kiss me.

Instead, he held out his hand. In it were the two other versions of the Firebird. “I’m going after Paul.”

“You—” My wavering voice, already strained from crying, broke. I had so many questions that I couldn’t even begin at first. “You still have the old prototypes? I thought you broke them down afterward.”

“That’s what Paul thought too. And—well, technically, always what your parents thought.” He hesitated. Even mentioning Dad, only a day after his death, hurt so terribly—for Theo nearly as much as for me. “But I kept the parts we didn’t reuse. Tinkered with them, borrowed some equipment from the Triad labs. Used the advances we made on the last Firebird to improve these two. There’s a decent shot one of these will work.”

A decent shot. Theo was about to take an incredible risk because it gave him a “decent shot” at avenging what Paul had done.

As funny as he’d always been, as flirty as we occasionally got, I’d sometimes wondered whether Theo Beck was full of crap underneath his indie band T-shirts and his hipster hat and the 1981 Pontiac he’d fixed up himself. Now I was ashamed to have ever doubted him.

“When people travel through dimensions,” he said, staring down at the prototypes, “they leave traces. Subatomic—okay, I’m gonna cut to the chase. The point is, I can go after Paul. No matter how often he jumps, how many dimensions he tries to move through, he’ll always leave a trace. And I know how to set these to follow that trace. Paul can run, but he can’t hide.”

The Firebirds glinted in his palm. They looked like odd, asymmetrical bronze lockets—maybe jewelry fashioned in the era of Art Nouveau, when organic shapes were all the rage. One of the metals inside was rare enough that it could only be mined in a single valley in the whole world, but anyone who didn’t know better would just think they were pretty. Instead the Firebirds were the keys to unlock the universe. No—the universes.

“Can you follow him anywhere?”

“Almost anywhere,” Theo answered, and he gave me a look. “You know the limits, right? You didn’t tune out every time we talked about this around the dinner table?”

“I know the limits,” I said, stung. “I meant, within those.”

“Then yeah.”

Living beings can only travel to dimensions where they already exist. A dimension where my parents never met? That’s a dimension I can never see. A dimension where I’m already dead? Can’t get there from here. Because when a person travels to another dimension, they actually materialize within their other self. Wherever that other version of you might be, whatever they’re doing: that’s where you are.

“What if Paul jumps somewhere you can’t follow?” I asked.

Theo shrugged. “I’ll end up in the next universe over, I guess. But it’s no big. When he jumps again, I’ll have a chance to pick up his trace from there.” His gaze was far away as he turned the Firebirds over in his palm.

To me it sounded like Paul’s best bet would be to keep jumping, as fast as he could, until he found a universe where none of the rest of us existed. Then he could remain there as long as he liked, without ever getting caught.

But the thing was, Paul wanted something besides destroying my parents. No matter what a creep he’d turned out to be, he wasn’t stupid. So I knew he wouldn’t do this out of sheer cruelty. If he’d just wanted money, he would have sold the device to somebody in his own dimension, not fled into another one.

Whatever he wanted, he couldn’t hide forever. Sooner or later, Paul would have to go after his true, secret goal. When he did, that was when we could catch him.

We could catch him. Not Theo alone—both of us. Theo held two prototypes in his hand.

The cool breeze ruffled my hair and made the lights flutter back and forth on the deck railing, like the plastic fish were trying to swim away. I said, “What happens if the Firebird doesn’t actually work?”

He scraped his Doc Martens against the old wood of the deck; a bit of it splintered away. “Well, it might not do anything. I might just stand there feeling stupid.”

“That’s the worst-case scenario?”

“No, the worst-case scenario involves me getting blended into so much atomic soup.”

“Theo—”

“Won’t happen,” he said, cocky as ever. “At least, I strongly doubt it.”

My voice was hardly more than a whisper. “But you’d take that risk. For Dad’s sake.”

Our eyes met as Theo said, “For all of you.”

I could hardly breathe.

But he glanced away after only a second, adding, “Like I said, it won’t happen. Probably either of these would work. I mean, I rebuilt them, and as we both know, I’m brilliant.”

“When you guys were talking about testing one of these, you said there was no way in hell any of you should even consider it.”