Would he end up like Vitaly Yurchenko, the one-time K.G.B. officer who defected to Washington exactly a quarter-century ago, revealed some of the deepest secrets of a collapsing empire, and then bolted from his C.I.A. handlers at a French restaurant in Georgetown and ended up back in Moscow?

The French restaurant is long gone; in one of those oddities of spy-vs.-spy history, it was just seven blocks south of the office block where Mr. Amiri took refuge Monday night in the Iranian interests section of the Pakistani Embassy.

But, remarkably, Mr. Yurchenko is still around. And as his interrogation by Iranian intelligence began on Friday, Mr. Amiri could only hope for the same fate.

Because there’s an alternate ending to such dramas that Mr. Amiri no doubt doesn’t want to think about. It is the case of Hussein Kamel, a son-in-law of Saddam Hussein. Mr Kamel escaped from Iraq to Jordan in 1995, and gave the West an insider’s view of Mr. Hussein’s then-active research projects on chemical, biological and other weaponry, not unlike the view of Iran’s nuclear program that American officials say they got from Mr. Amiri. Mr. Kamel, too, went back home, promised by his father-in-law’s lieutenants that all was forgiven. He was shot a few days later.

From afar, it appears that the Iranians are still uncertain which model should best apply to the bizarre case of Shahram Amiri.

Viewed one way, Mr. Amiri’s decision to return is a huge propaganda boon for the Iranians. For months they have insisted that Mr. Amiri was kidnapped in Saudi Arabia in June 2009, by the C.I.A. and Saudi intelligence, then drugged and tortured into making up stories about Iran’s covert nuclear program. “I was under the harshest mental and physical torture,” Mr. Amiri said when he landed in Tehran, an account American officials dismissed as a “fantasy” spun to save his life.

Viewed another way, the Amiri case must be deeply unsettling to the Iranians. If you believe only part of the American version of events — the part that claims that the 32-year-old specialist in radiation safety provided information for a few years to the C.I.A., then voluntarily defected and spilled even more — then Iran’s leaders have to wonder about the latest penetration of their program and how deeply it has been compromised.

All of which must make it hard to decide how to deal with Mr. Amiri’s return. “We first have to see what has happened in these two years and then we will determine if he’s a hero or not,” Manouchehr Mottaki, Iran’s foreign minister, said in Portugal on Thursday.

As Ray Takeyh, a scholar at the Council on Foreign Relations, notes, there are no real Iranian precedents for dealing with returning nuclear defectors. “I think they have a Soviet approach — they will want to make propaganda use of him,” Mr. Takeyh said. “My impression is that he will be around for a year or so.” But then, he said, “I don’t think it’s going to turn out well for him. They have to establish to other potential defectors that there is a cost to be paid.”

On this side of the Atlantic, meanwhile, one mystery in this bizarre case is why, after Mr. Amiri rejected the pleas of American officials to stay in the United States as a $5 million ward of the C.I.A., American officials were suddenly willing to talk about his role.

After all, for a year American and European officials had pretty uniformly responded to questions about him with blank stares. A few allowed that he had offered up insights into how Iran had hidden various research projects and facilities, some based inside the university where he worked.

Now it appears that he offered some insight into the covert world created by Mohsen Fakhrizadeh, a scientist who is almost an obsession on the campus of the C.I.A. Mr. Fakhrizadeh, who is named in a United Nations sanctions resolution against Iran, was the head of what were once known as Project 110 and Project 111,believed to be code names for Iran’s efforts to design nuclear weapons that could fit on missiles.

It is possible that American officials began to talk about Mr. Amiri last week simply to defend their handling of the case. “This is clearly one that went bad,” a senior administration official said on Friday. “I don’t know whether that’s because the agency mishandled it, or whether it’s because the guy was a bit unstable.”

It’s also possible, as many in the blogosphere have speculated, that Mr. Amiri was a double agent, sent by Iran to spread disinformation. That, however, seems unlikely, since American officials insist that most of his information checked out. And had they believed that he was a double, it’s unlikely that he would have been allowed to return to Iran.

Now that he’s back in Tehran, of course, the Iranians have to worry that Mr. Amiri could be an American double agent. But that also seems unlikely. As Mr. Takeyh says, “Who would trust him enough to let him inside the program again?” Just ask Mr. Yurchenko: the former K.G.B. agent was grilled for years about what he knew and, more important, what he told the Americans.

At best, Mr. Amiri seems headed to the same kind of multiyear interrogation. His hope, of course, is that he will be able to live long enough to tell the whole, complicated tale of his mysterious travels to his young son — when the son is old enough to understand it, and maybe when the world finds out whether Iran was racing for the bomb or gave up trying.