Luca, a young sea monster, is overjoyed to be reunited with his best friend, Alberto. The two young monsters are looking forward to another summer full of pasta, gelato, scooter rides, and swimming. But then they are woken up by their screaming neighbor. Apparently, a monster (not the sea variety) is scaring kids at night. After Alberto and Luca volunteer to find out why, one thing leads to another and they end up in another world. This world is full of monsters who have made an entire business out of scaring human children. Luca and Alberto need to both blend in and find a way home. Luckily, they find help in the company's best Scare Team: James P. Sullivan and Mike Wazowski. But will the boys be able to keep their secret?

It was an attack that started it all. An attack that cost over 300 years of life. 300 years they could've done something to stop the destruction of their home, the fall of the union, the end of their fame. But there was nothing they could've done. Now no one remembers them. ((Rated T for violence and language))