Bound by a shared destiny, a teen bursting with scientific curiosity and a former boy-genius inventor embark on a mission to unearth the secrets of a place somewhere in time and space that exists in their collective memory.

In a gritty and alternate 1985 the glory days of costumed vigilantes have been brought to a close by a government crackdown, but after one of the masked veterans is brutally murdered, an investigation into the killer is initiated. The reunited heroes set out to prevent their own destruction, but in doing so uncover a sinister plot that puts all of humanity in grave danger.

The Heffley family attends a party at a roller rink, where Greg Heffley reunites with his best friend List of Diary of a Wimpy Kid characters#Rowley Jefferson, meets a new girl at school named List of Diary of a Wimpy Kid characters#Holly Elizabeth Hills who Greg instantly has a crush on, and reveals he passed on the Cheese Touch. During the party, his older brother List of Diary of a Wimpy Kid characters#Rodrick Heffley advises Greg to ask Holly to skate with him when Couples Skate begins and then interferes with Couples Skate by persuading a crowd of hooligans to enter the rink, along with replacing "Always (Atlantic Starr song)" by Atlantic Starr with a heavy metal music song. This prompts Greg's parents, List of Diary of a Wimpy Kid characters#Frank Heffley and List of Diary of a Wimpy Kid characters#Susan Heffley (who misunderstand this) to speak to Greg on the rink's public address system and then carry him off the rink. Greg, extremely angry with Rodrick for humiliating him, tries to tackle him, but he misses and in turn, lands in a little girl's birthday cake. She and her friends then furiously proceed to beat up Greg as the intro starts.