I Know What You Did Last Sleepover is the sixth episode in Season 1 of Sydney to the Max. It first aired on March 8, 2019, to 0.52 million viewers.
Sydney and Olive are excited about their weeklong sleepover, but they discover each others' strange habits which cause a rift between the two. Meanwhile, in the past, Young Max and Leo get into a fight about Max constantly forgetting his job responsibilities at the arcade.
Sydney and Olive tell Max that Olive's parents were leaving for a week and that she could stay with them at home. Max doubts, but finally gives them permission. Then Olive arrives and moves into the house. She spends the day with Sydney. At night, when they are in her room Max tells them that they should go to sleep. But Olive talked to Sydney and didn't let her sleep. So she makes her dad come and tell them to fall asleep. He does it and leaves, but when Sydney tries to sleep, Olive lies down in his bed and talks to her with whispers. The next morning, Olive waited to use the bathroom, but that Sydney was there for a long time, so she couldn't get into the bathroom. Then, during breakfast, Sydney sees that Olive was wearing her brand-new shirt, that annoyed her, but told her that was fine. Later, in Sydney's room, Olive tried to do her homework, but Sydney was practicing bass and making noise. Olive makes Max tell him to use the headphones when she plays, but then Sydney makes Olive put them on so she can listen to her. Later on, Sydney speaks with Max about that she did not like Olive's habits, so Max proposes that they have a game night. At night, the Sydney and Judy team beat Olive and Max, so when it comes Sydney Sydney's turn distracts her to fail. Sydney gets upset and tells her she can't change the rules. Then they both discuss what they don't like about each other and in the end Sydney leaves angry. The next day, Max tells Sydney that she should talk and fix the problems with Olive before she leaves. Judy talks to Olive. So when they believe that Olive's parents' car arrived to take her away,she takes a long time to leave, walks slowly, she and Sydney had trouble talking to each other. Then Sydney finally talks to her apologizing to her, they talk about what happened and they reconcile. Then Max appears and says that Olive would not leave yet, because his parents' flight was delayed. They realize that the stretch is to make up.
Max was late to work at Just Fun and Games, since he spent time with the Dog Boys, Leo got mad at him, as he always did and gave that excuse. Then fire him. Max leaves annoying, because he thought a friend didn't do that. Later, he talks with Judy and she tells him that he should apologize to Leo. Max goes to Just Fun and Games to apologize to Leo, but then Max sees that he had already hired a boy. Later, it was raining and Max was bored in his room without Leo, Judy enters and tries to cheer him up, then sees Leo's things in a box and tells Max to call Leo to come and take them away. Later, Leo arrives, Judy tells Max and leaves them. They both see the things that were in the box, they remember what they did together as friends, so they apologize to each other for what happened and become friends again.