Scoop, Muck, Lofty and the rest of the gang can’t wait to help Bob with his biggest build ever – building a dam and transforming an old quarry into a reservoir to provide Spring City with fresh water. Bob enlists the help of another builder, Conrad, to help clear the quarry – along with his three enormous Mega Machines, Thud, Crunch and Ace. Conrad, secretly resentful that he lost out on the dam-building contract to Bob, plots to undermine his rival’s reputation and sabotages the dam. Soon Bob realizes that things are not as they should be… and that it’s up to him and his team to save Spring City!