Elliot is grown-up and getting married. He and his family invite E.T. to the wedding. Coincidentally at the same time that two other colonies of aliens are about to invade the earth. One is a colony of big brained aliens who are so disgusted with the Earth they decide to overrule it. Also deadly aliens who are mal-breds of E.T's benignity, invade Redwood Forests and are after E.T.
E.T. returns to Earth to locate a cure for a plague of illness the people of his home planet have contracted. Elliot and Keys discover it in the form of a specific plant which grows in South Africa. Thus they take the next flight there to retrieve the plant, and also end up finding out more than what came for in Africa.