When his jailers barged in before dawn, the captive thought it was the end.

For eight years, he had been held in a windowless cell of an underground prison, dark night without end. Now, the guards ordered him to finish his prayer, then removed the thick blindfold and metal handcuffs he had almost always worn and tied his wrists with cloth — leaving nothing to incriminate them, he thought, if his body was later found floating in a river or lying in a ditch. They bundled their captive onto the floor of a minivan, hiding him under the weight of two men, and set out for an hour’s drive.

But unlike many other political prisoners before him in Bangladesh, Mir Ahmad Quasem Arman was not being taken to his death and disposal. Instead, he said, he was dropped off in a barren field on the edge of Dhaka, the capital.

A lot had changed: new highway overpasses, a recently opened subway system. But Mr. Arman was unaware of the latest and biggest change of all. Sheikh Hasina, the prime minister who had ruled with an iron fist and vengeful designs for the past 15 years, had fled the country as protesters stormed her home.

With her exit on Aug. 5 came the reappearance of Mr. Arman and two other men long confined in the secret prison.

Mr. Arman had been a spoiled and chubby-cheeked lawyer when he disappeared at the hands of paramilitary forces in 2016 — under no criminal accusation himself, but seemingly held accountable for his father’s decades as an Islamist activist and business magnate.