Something is happening here... but you don't know what it is.

It's May 17, 1966 and Bob Dylan is playing Manchester Free Trade Hall.

He is coming to the end of one of rock's great periods of creativity, courage and sheer visionary bloody-mindedness. It's a few days before his 25th birthday and a few weeks before the motorcycle accident that would see him retire to his tent, emerging bearded and oblique like an Old Testament prophet.

That was the immediate future, but the Dylan of 1965 and 1966 was about the immediate present: going electric, never looking back, alienating those who had revered him in a search for something bigger and truer. It was a move of epic, ground-breaking proportions.

His performance at Newport in 1965 had scandalised colleagues and fans in the folk movement, who thought their idol had sold out by plugging in. Electricity was, apparently, anathema to the folk crowd who, despite often preaching a message of revolution both personal and political, turned out to be quite reactionary when it came to music. Rock n roll and folk were not to mix. They were to be kept apart for fear of the loud one polluting the acoustic polemic with its bawdy noise.

He had hooked up with members of primo Canuck rockers The Hawks during the Fall of 1965 for a tour of the US. Fuelled by genius, conviction, courage and a healthy intake of amphetamines, Dylan played date after date in front of crowds who responded with varying degrees of bemusement and anger to his new direction. On his days off, he recorded Blonde On Blonde. It completed a triumvirate - with Another Side Of Bob Dylan and Highway 61 Revisited - of burning brilliance in just eight months.

By the Spring, he was in England for a series of gigs including Manchester. The famous bootleg was incorrectly identified as having been at London's Albert Hall, but it was in Lancashire that maybe rock's most famous-ever heckle was heard.

Dylan played, as was his wont, an acoustic set that included an excellent Visions Of Johanna and other material from the forthcoming Blonde On Blonde, as well as something for the core constituency in Mr Tambourine Man. It's a decent performance, but you can sense that he is marking time until the second half of the set.

A barnstorming, rolling, tight and powerful Tell Me Momma kicks things off - a much underrated and surprisingly unreleased song. The band are precise and driving, the vocal wild and uplifting. He introduces the next song I Don't Believe You (She Acts Like We Never Have Met) with an arch, but sort of conciliatory, "it used to go like that, now it goes like this". The set builds to a sneering, sinister Ballad Of A Thin Man.

Then comes the famous heckle: "Judas!" which draws a medium-sized smattering of applause from some of the audience. Looking back, it's striking how reactionary people could be - especially those who saw themselves at the vanguard of a movement that was all about change.

"I don't believe you," shouts Dylan. "You're a liar!"

A very Dylan retort: at once totally confusing, powerfully simple and totally assured.

Turning to Robbie Robertson and company, he snarls: "Play fucking loud" and they launch into a swirling, vicious version of Like A Rolling Stone. It feels like he is singing at everyone who stands in his way, anything that would stop him always moving forward. It is an artistic statement of the highest order; that the artist will not pander to his audience and must follow his own path regardless.

It's a song totally about its time - the struggle and possibilities of the mid-Sixties - and yet timeless, bigger than history even. The performance crystallises not only his brilliance, but his verve, determination and sheer balls. Folk had gone electric. Dylan was electric. Rock n roll was forever changed.

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