The whereabouts of the much-fabled banjo has been a mystery more than 50 years.
The last time anybody saw or heard of the banjo was before Lennon's beloved mother Julia was killed in a road accident in Woolton, Merseyside, in 1958.
But now author and playwright Rob Fennah is on a personal quest to locate it.
In a new novel, Julia's Banjo, Rob, 47, from Crosby, Merseyside, tells the little-known story of a teenage Lennon learning how to play his Rock 'n' Roll favourites with his mother Julia.
The book tells the fictional story of Beatles tour guide, Barry Seddon, who finds a letter giving him clues to the location of the banjo before ruthless Texan antique dealer Travis Lawton hears about the priceless relic and a drama ensues.
In real life, for more than a decade Mr Fennah has combed through car boot sales and dusty attics in a bid to find the 'catalyst that changed the world'.
Now he is urging people in Liverpool to rummage through their wardrobes and attics to check whether 'Julia's banjo' banjo could be lurking unacknowledged.
He said: "It was originally bought by John's maternal grandfather George Ernest Stanley and Julia inherited it from him.
"I suspect that one of John's realtives gave it away after Julia's death and that somebody in Liverpool has got it, without realising just how important and valuable it is.
If found, the banjo would be worth several million pounds at auction
"It could have been passed-on or sold many times since it was last in John's hands, but it's a very distinctive instrument, with a mother-of-pearl back.
"If it is found, it will be a question of proving the provenance, but John's sister Julia may yet be able to recognise it."
Rob explained how he became interested in the fate of the banjo.
He said: "A piano formerly owned by John Lennon fetched a cool one and a half million pounds at a Sotheby's auction.
"At a Beatles convention I was chatting to Allan Williams - the band's first manager about it - and a dealer listening-in to our conversation perked up and said, 'that's nothing compared to what Julia's banjo would fetch'.
"The dealer went on to tell me how Julia Lennon introduced her son to the world of music by teaching him to play Buddy Holly's classic That’ll Be The Day."
Rob believes that the banjo is waiting to be discovered.
He added: "If anyone has this banjo and it can be proved to be John Lennon's they, they are sitting on a fortune.
"It's the Holy Grail of pop memorabilia and I am sure it would fetch several million pounds at auction."