He got a message from a family friend, a Mrs Dryhurst, whom he had asked for help before he left: "Don't let the ship sink for a ha'porth of tar." He didn't understand what she meant. She sent a second note, passed on by the Nationalist representative. It told David the name and address of the hotel where his father was staying.

When father and son met they hardly spoke. They had breakfast and left. One question in the train to Calais was: "Are you armed?" "No, Edward." (He didn't call him "father".)

Savarkar was duly deported and spent 14 years in jail in the Andaman Islands. After his release he became a prominent campaigner for independence. Garnett, who never saw him again, was rescued from folly by a chain of friends. Mrs Dryhurst told Mabel Hobson, she told her brother, the future theatre critic Harold, and both told their parents. At the Hobsons' message Connie collapsed but Edward managed to get himself across the Channel. When the police did discover David's aborted plan, they tightened up their procedures but no officer interviewed the 17-year-old student from Hampstead. The well-known family escaped unscathed, as they never could today.

David maintained his political radicalism at least until he got married, in 1921. During the Russian Civil War he was "violently opposed to British intervention in Russia" and loudly proclaimed that he "did not know a single Conservative MP". He was proud, in retrospect, of his "innocence and sincerity", and also of his conspiratorial intelligence, for, aged 50, he was sure his Brixton end of the plot would have worked. But by the time Lady into Fox, a beautiful piece of English pastoral, later danced by the Ballet Rambert, was written, he had found his social place and subsided.

None of us knows what makes a terrorist, only that it involves what Garnett called "lack of a sense of reality". Non-integration is a factor. All the fact and fiction that gets written about terrorism picks it up, but what remains unfathomable is the moment of dropping out. Why do some youngsters when they abandon home ties take up the violent cause? What David Garnett dipped a toe into one summer Osama bin Laden, another privileged son of a wealthy family, pursued for nearly 20 years a century later. All the intimate circle of would-be bombers in Doris Lessing's 1985 novel The Good Terrorist were, in the Thatcher era, dropouts alienated from their parents and trying to conceal their middle-class voices. The 1997 novel American Pastoral, which helped Philip Roth to win the Man Booker International prize recently, tells the story of a teenage girl bomber through her father's eyes: a father who was never absent and just can't fathom what he did wrong.