As far as that plot goes, here is the information on the new book provided by Ian Fleming Publications:
Anthony Horowitz’s second James Bond novel using original material by Ian Fleming will be published on Thursday 31 May 2018, it is announced today. Forever and a Day is a prequel to Casino Royale, Fleming’s first 007 novel, and will explore the origins of the world’s most famous secret agent.‘M laid down his pipe and stared at it tetchily. “We have no choice. We’re just going to bring forward this other chap you’ve been preparing. But you didn’t tell me his name.”“It’s Bond, sir,” the Chief of Staff replied.“James Bond.”’The sea keeps its secrets. But not this time.One body. Three bullets. 007 floats in the waters of Marseille, killed by an unknown hand.It’s time for a new agent to step up. Time for a new weapon in the war against organised crime.It’s time for James Bond to earn his licence to kill.This is the story of the birth of a legend, in the brutal underworld of the French Riviera.
Forever and a Day by Anthony Horowitz will be published May 31, 2018 in the UK by Jonathan Cape, the original publisher of Ian Fleming's James Bond novels and now an imprint of Vintage Publishing. It's available for pre-order from Amazon.co.uk. There's no word yet on who the U.S. publisher will be come Fall, but Trigger Mortis was published here by Harper Collins, as was Horowitz's most recent novel, his clever twist on Agatha Christie-style murder mysteries Magpie Murders (whose U.S. publication was also substantially delayed from its UK debut), so I'd say they seem like a good bet.