He catches on right away. “Coordinates?”

Katie waves her pencil-smudged fingertips. “I’m still sitting here.”

“It’s a tweet I found that led me to the attack. The thirteenth one. Hashtag thirteen was one of the searches Adam’s program had been running.”

“I wrote an algorithm, though not my best one.” He smirks. “But still impressive. I basically set it up for social media mining so that it would extract keywords, patterns, phrases—whatever Lia was looking for from a dozen or so different sites. Didn’t filter very well.” He turns to me. “Which means you’ve spent more time than I can possibly imagine sifting through that raw data.”

I hold my poker face, concealing just how many hours were consumed every night for the last couple years.

“But, unlike Lia’s haphazard approach, it was carefully planned and well-hidden.”

“Nine one is the date.” I address the paper. “Followed by time, latitude, and longitude of Navy Pier.”

I think of how vindicated I was when I found it. Then I think of the way the CPD hotline receptionist thanked me for my call and said she’d pass it along to a detective, like I was some delusional little kid.

“I called the police. I tried to warn them.” I glance at Katie, wondering if she dismissed my warnings as obsessed and unhinged like they did. What does she think of me now?

“Please,” I say to Adam. “Will you figure out where it came from?” I hold my breath, waiting for his response as Adam examines the tweet like there’s more to it.

Sophomore year, he hacked our school’s emergency system and 64 sent texts to all the parents saying school was cancelled. Even more impressive, he was never caught. He called it white hat work, justified because we should’ve had the day off. The roads were ridiculous. As far as I know, I’m the only one he ever told.

“Lia—” he starts in his lecture tone.

I cut him off. “The IP address could lead to the guy who sent the tweet or maybe the guy organizing the whole Swarm.” I can’t look him in the eye. “I’ll turn it over to a detective. I just need to know what it is first. They had leads in my dad’s case and never arrested anyone.”

Adam’s face remains hard.

I think of Jeremiah Dopney in ICU across the city. Fighting to stay alive. My voice breaks. “This can’t all be for nothing.”

While I wring my hands beneath the table, I focus on Adam’s black hair, perfectly molded into several peaks atop his head.

His eyes narrow. “I will do this for you on two conditions.”

My lips flicker, and I try not to smile.

“Don’t use the program again. Clear it from your device.”

“You said it was untraceable.”