Alexander's day begins with gum stuck in his hair, followed by more calamities. Though he finds little sympathy from his family and begins to wonder if bad things only happen to him, his mom, dad, brother, and sister all find themselves living through their own terrible, horrible, no good, very bad day.

Through a series of misunderstandings, Alvin, Simon and Theodore come to believe that Dave is going to propose to his new girlfriend in New York City - and dump them. They have three days to get to him and stop the proposal.

Belle, her little sister, and her comatose twin brother move into a new house with their single mother in order to save money to help pay for her brother's expensive healthcare. But when strange phenomena begin to occur including the miraculous recovery of her brother, Belle begins to suspect her mother isn't telling her everything and soon learns they moved into the infamous Amityville house.