https://www.gamespot.com/articles/fortnite-update-season-4-new-skins-map-changes-due/1100-6458631/

In Save the World, part one of a new Blockbuster Event has been added with the new update. This event sees you "join Spitfire and Lok as they investigate the comet and gear up to recruit a team of superheroes!" For more details, check out the official patch notes below, via Epic Games.