Charlie and Lola's summer fun takes a nosedive when Lola refuses to talk to their neighbor, Arnold Wolf, after he dumps her ice cream cone on the ground.
Lola brings the class guinea pig, Bert, home during summer vacation, and when she and her brother Charlie build a guinea pig run, he escapes, causing them to search everywhere until they find that Bert has surprisingly given birth to babies.
Lola and Lotta convince Charlie's friend Marv that they can look after his dog Sizzles while they are all at the park, but the girls actually know less about dogs than they think they do.
Lola is determined to help her brother have an extremely happy birthday, but her idea of birthday fun and decorations does not fit well with Charlie's monster-themed party.
Lola is proud that she can do everything on her own and wants to do everything alone, but her brother Charlie explains that sometimes it is better to do things with others.