Tim walks. For no discernible reason, he walks. He's taken by the compulsion to walk, to keep going, to not break stride for any reason--it doesn't matter if he's in conversation, if he's tired, if he wants to stop to buy a sandwich. At the end of his walks, he calls his wife for a ride home from wherever his body took him this time. 
 Skimming the reviews here, I feel like I'm just about the only person who liked this--though I'm in the minority who wasn't wowed by Then We Came to the End. Like Tim, the book starts with a straightforward progression and then begins to meander, taking tangents and revisiting old topics seemingly at random, an obvious parallel to Tim's worsening condition. 
 Waffling between 4/5 stars; erring toward five because this is the first book I've enjoyed so completely in a long time.