"Do you think it'll work?" Dean asked desperately.

"Well, I don't know," the old man said dubiously. "I mean, it should, the numbers are right, the premise is solid, and genetically, your brother's just about the strongest match I've ever seen." His voice trailed off.

"You're not really filling me with confidence here, Doc," Dean said, clenching his fists together to hide their shaking.

The doctor looked at him pityingly. "I'm sorry, son. I know you want a cast-iron guarantee, but there just isn't one. All we can do is our best. And hope."

"Hope what?"

"That Sam wakes up."