Suspicions Are Aroused

So I stepped outside last night at about 12. I was nearly scared out of my wits when I saw Aleck Smart sitting on the roof. His finger to his lips, and signaling for me to climb up the ladder and join him.
"What are you doing here?" I whispered after I had reached him.
"Sitting on a roof." he replied, "but assuming you're wondering why I'm here, it's to deliver some grave news."
My thoughts flew to Vanderdecken.
"Not Vanderdecken." he assured me, "it's somebody here."
"Why?"
"I intercepted a phone call. I'm surprised you didn't notice it."
"I've been busy," I shrugged.
"The contents were rather interesting," he said, "Somebody here is our enemy."
"You're kidding."
"I do not kid." he shook his head, "the contents of the message were made with a voice scrambler, so I can't identify who it was. It was also made using your cell phone, which I have noticed you carelessly leave on the table, so it could easily have been grabbed."
"You've been watching me?"
"Only for today, but by the way you toss it, I can tell that you are quite accustomed to doing so."
"What did the message say?"
"That they had identified you as the target, and would continue to observe you."
" 'observe'?"
"Yes, the person on the other side explicitly stated that you are not to be harmed, or allowed to discover their goal."
"Do you know what that goal is?"
"No, but I doubt it's world peace."
"Any theories?"
"Possibly you are working on something or have something technologically valuable to them."
I nodded, "possibly, but I'm not working on anything too amazing right now."
"Regardless. As for who it is, it could easily be any of the adults there."
"18 people." I pointed out.
He shook his head, "twenty-seven. Nine of your cousins are adults."
"Oh yeah."
"I know this won't be easy for you. I wish you had somebody on the inside that they wouldn't suspect. Are all your family here?"
"No, there's still one more family."
"The Carnegies?"
"Yes,"
"Oldest is...15, I believe?"
I nodded.
"Try to tell him what's going on, see if you can get him to work with you."
"I remember him from last year. He'll help."
"OK, good. Have him help look for anything suspicious, and to watch your back. And Ben?"
"Yes?"
"Be careful. I don't want to lose you too."