In There Will Be Fire (Putnam, Apr.), journalist Carroll details a 1984 IRA plot that came close to assassinating British prime minister Margaret Thatcher.

How did the IRA manage to smuggle a bomb into the hotel where Thatcher was staying?

There was a failure of imagination on the part of the British. They knew that the IRA had this technology. They knew that they had skilled operators to use it. And yet, for this particular conference, the focus of the British police was the coal miners who were striking—their focus was on barriers around the hotel, and it didn’t really occur to them that the hotel itself needed a thorough search. But this was a more innocent era, in a way, because such a thing had never happened before. Sometimes it’s difficult for human beings to anticipate something completely new.

How close did Thatcher come to dying?

Had she been in her bathroom at the time of the blast, or had the five tons of Victorian masonry that was initially falling down towards her suite not swerved, she’d have been killed.

How would history have changed had the bombing succeeded?

Thatcherism was still just a budding ideology in 1984. She’d won a second term, but the radical domestic revolution that she’d wanted to unleash had not really happened. Had she died, Thatcherism may well have died with her, because we just don’t know who would have replaced her. And with Anglo-Irish relations, things could have been so completely different. This had been Britain’s 9/11 moment, in some ways, given the shock of it, and yet, to her eternal credit, she was very restrained in her reaction.

In what way?

There was no unleashing of the security forces to go hunting for the plotters, no mass revenge, no mass internments without trial. Not only that, but she proceeded to sign, a year later, the Anglo-Irish agreement, a historic treaty between the Republic of Ireland and the U.K. that paved the way for the Good Friday Agreement 15 years later.

Did Sinn Féin president Gerry Adams approve of the assassination plot?

There is no proof that he did, and I don’t say in the book explicitly that he knew in advance. However, he was a member then of the IRA’s Army Council, which directed strategy. The Army Council would have had to have, for an attack of this scale, known about this in advance. Not necessarily all the details, but they would have had to green-light the operation.