Junius died in 1852, just as Edwin’s career was beginning. In 1855, John made his debut. Over time, he established himself 

as a fiery, physical performer. He did well. But, unlike Edwin, he never felt the stage was his calling. He thought he was destined for ­something greater.

And what of the girls? Rosalie was awkward and infirm, but Asia could probably have made a go of it. She had a flair for the dramatic.

In their childhood productions, she’d been Juliet to Edwin’s Romeo. She performed a scene at school, playing both Richard III and Lady Anne. But she despised actresses; said they were women who made love in public for money. She managed somehow to idolise her father and brothers while simultaneously despising the women they worked with. She married an actor. But when Edwin married an actress, she accused him of sullying the family name. Her furious antipathy towards his wife caused a rift that was long in healing.

Asia was a writer. She wrote a book about her father and another about Edwin. Her final book was about John. It was written nine years after John was captured and killed. Her love for him is made so evident, 50 years passed before anyone dared publish it.

This book makes clear that Asia knew, as others in the family did not, of the work John was doing for the South, meeting in secret with Confederate sympathisers, and smuggling them into Virginia. She can’t have suspected what was to come, but she did see that plots and conspiracies surrounded him. She does her best to condemn her brother’s terrible crime. But she slips in some blame for Lincoln, too. With the war so recently over, the suffering so extreme, he had no business going to the theatre, she writes. He should have gone to church. If Lincoln hadn’t demeaned himself with low entertainments, he wouldn’t have died.

The Booths witnessed many of the era’s great (and dreadful) events. John visited John Brown as he sat in his cell awaiting his hanging. Rosalie, Edwin and John were all in New York during the draft riots. While mobs close by murdered Union sympathisers and black residents, the Booths had a black man hiding in their basement, a Union soldier convalescing upstairs.

By then, John was becoming a concern to his family. The others were not political. They supported the Union. Most of them opposed slavery. But their muted opinions were no match for John’s increasing fanaticism. When Edwin boasted that he’d voted for Lincoln, John lost his mind. There was a terrible fight. Edwin threw John out of the house and John swore he would never return.

He did come back, though only once, to appear with his brothers in a benefit performance of Julius Caesar. Never before had the three shared the same stage. The year was 1864; the assassination a mere five months away. June was Cassius. John wanted to be Brutus, but Edwin took that part, relegating John to Mark Antony. Few in the audience noticed an added line to Antony’s famous speech. “Sic semper tyrannis.” John was rehearsing.