Disclaimer: I don't own Divergent (or Allegiant); Veronica Roth does. Christina's line of dialogue directly from the book comes from the hardcover edition, page 507.
I didn't believe it. Matthew said he saw him do it, said he saw him take the truck, take the serum, and go, but Tobias - he wouldn't. It's the coward's way out, and his name wouldn't have been Four if he were a coward. I knew I had to go after him.
The trouble happened when I got there and realized that it was just him, alone in that house, and it was just me - I had to stop him. And we'd never gotten along all that well under the best of circumstances. But Tris's face floated before me, and I knew I had to try.
"Tobias!" I called out louder than I'd intended, and he jumped. The look he gave me was the look I'd expected to get, but it made me sad all the same. He was no longer the person who'd seemed to believe that anything was possible. It was like all hope had gone out of him when we'd lost Tris. But I forged ahead.
"Matthew told me - he told me you'd stolen some serum and a truck. I didn't want to believe that."
He looked at me for a long moment and then held up the vial, clutched tightly in his hand.
"Believe it," he said flatly. "And don't try to stop me. This isn't your decision."
I sighed. "I know it isn't - but I don't think you really want it to be yours either. Maybe right now you do - but it's not what Tris would want, and I don't really think it's what you want. You want to forget her? Do you think that would be the fate she deserves?"
I may be Dauntless now, but my Candor roots have never left me, and I knew I'd hit a nerve. It was pretty obvious when Tobias stepped toward me, and his voice rose as he shouted that I was wrong, that I didn't know her at all and how did I know what she'd want. While I probably should have been scared - he was capable of anything at this point - I was just angry. This wasn't the person Tris had loved, and I wanted that person to come back. That was the person who would mourn my friend with me.
I don't even know what I said. I know I called him a coward and mocked him for even threatening me the littlest bit. And that was when he deflated. He apologized and stared at the floor, leaving me wondering what to say.
We stood in silence for a minute. Without his anger, Tobias looked more vulnerable than I'd seen him, and that wasn't something I was prepared for yet. That wasn't why I'd come here, to be that sounding board. I'd just wanted to stop him before he made a decision he'd regret, and it seemed that I might have done that. I didn't know if he'd want me to see him look this way. But he didn't even seem to be aware that I was still there, so I waited a moment before letting out a deep breath and stepping closer to him. He was still holding the vial, and I didn't try to take it - I just wrapped my hand around his and said "The person you became with her is worth being. If you swallow that serum, you'll never be able to find your way back to him."
I'm still not sure what did it, but Tobias's face crumpled at that moment, and the tears started flowing down his cheeks. I'd seen him in tears once or twice already, but they had come and gone quickly, and he'd left those rooms just as soon as he could. This time, something was different, and I knew somehow that he was hurting more than he'd yet to let himself. Without thinking of what I was doing, I wrapped my arms around him, unsure if he would allow this or just push me away. There was a single moment of tension, and then he just collapsed against me, his shoulders heaving with the sobs he'd finally given in to. That much was clear, and I held on tightly, trying to swallow the lump in my throat, somehow knowing that this was just the first of many conversations we'd be likely to have, and I had no idea for how long they'd go on. But I couldn't cry yet. I wanted to, but he needed this more right then.