Along the way he kept thinking the carriage was about to be robbed or he was about to be killed, despite all evidence to the contrary.
No one is ready for his return, since it's so late that they assumed he would stay overnight somewhere and come the next day.
Dorrit finds Amy and Frederick Dorrit sitting together and gets jealous. Amy is telling Frederick that he seems younger, and her uncle says that it's all due to her.
They realize that Dorrit is there and are thrilled to see him.
But when Amy asks if he's tired, he gets really mad. He sends Frederick off to bed, saying that he is far too old and feeble to be awake.
He suddenly falls asleep for a minute or two. Then he wakes up again with a start and complains about how no one has wanted him to come back. Then he kind of randomly prattles on about what London was like and asks about Mrs. Merdle.
Amy tells him that Mrs. Merdle is throwing a grand farewell dinner since she is returning to London, and they are of course invited.
The next morning Dorrit is extra nice to Mrs. General, but he keeps weirdly falling asleep during breakfast.
After breakfast Dorrit starts in on some sweet nothings, and after a little while, Mrs. General says that they'll continue this another time. She's doing a fake hard-to-get act.
Dorrit is clearly not OK but keeps getting angry any time anyone brings it up.
The day of the party, Dorrit puts himself together but looks old and worn.
Amy loses him in the crowd and suddenly gets a note from Mrs. Merdle saying that he is not well.
When she finds him, Dorrit has totally snapped. He's talking to Mrs. Merdle's guests as though he were still in prison at the Marshalsea and is giving a tour of it. He is totally confused and wants to see a turnkey who has been dead many years.
Finally Amy gets him out of there.
He never regains his mental faculties. (Shmoop's going with stroke as the diagnosis for this one, but of course Shmoop is neither a doctor nor plays one on TV. Still, that's what it sounds like.)
Dorrit continues to think that it's long ago and he's in prison. He doesn't recognize Mrs. General. He only wants Amy. At one point he starts giving her his jewelry and clothes to take to a pawnshop, which she pretends to do.
And then, at long last, he dies.
What a totally depressing end.
His brother Frederick is overcome with grief and cannot believe that he has outlived him.
Finally Amy goes to bed, for the first time in ten days. Frederick stays behind to pray and cry over the dead body. He dies in this position a few minutes later.