Solution—

This time when Charlie disappeared into P vs. NP, Don didn't try to stop him. Instead, he joined him, at least in the garage. He sat for hours watching Charlie work, chalk dust hanging thick in the air as Charlie tried to find the answer to the unanswerable.

Don spent his days doing the same – going through every case Colby had worked on, every file that he'd touched. There were no answers to be found there, either.

After work, he came here, instead of home. He made sure Charlie ate and slept, at least some. He himself used the foldout cot, sleeping to the never-ending clack of Charlie's writing.

Will also spent time with Charlie. He sat next to Don and read or coaxed Don into a quiet game of cards. Nena, thankfully, was on a trip with her mother. Alan appeared at regular intervals, offering food or extra blankets, but wouldn't set foot inside the garage.

Charlie grew gaunt and haggard, in spite of Don's efforts. Though he used to annoy him, Don now longed for the return of Smug Charlie, flush with proving once again his superiority over ordinary mortals. He would even take Whiny Charlie, complaining about housework, or Greedy Charlie, sucking up the attention of all around him. Anyone but this hollow, driven man who had to be forced to eat and cried silently in his sleep.

But he didn't disturb him. No one did. It seemed everyone was holding their breath, hoping against reason that Charlie would find a solution to the impossible problem. That somewhere in P vs. NP would be the answer to Colby's lies, his treason explained in the numbers that sprawled across the chalkboards.

So Don watched, and prayed that somehow Charlie could find the answer that would save them all.