Professor Philip Brainard (Robin Williams) is experimenting with new kinds of energy, and he thinks this project will save struggling Medfield College, where his girlfriend, Sara (Marcia Gay Harden), is president. But when he discovers a lively, rubber-like substance dubbed flubber, he gets so excited, he absent-mindedly misses his own wedding. Sara dumps him, so he tries to use his discovery to win her back; unfortunately, the mischievous flubber seems to have a mind of its own.