The Please Don't Tell My Parents series is a great series about a middle-school (now high school freshman) collection of supervillains who are too nice to be bad guys but too mischievous to be heroes. The books have very low stakes, for the most part, and are really more about exploring the complicated network of lovable weirdos which exist in the Los Angeles superhuman world.
The last book, I Did Not Give That Spider Superhuman Intelligence was unrelated to the main series' adventures of the Inscrutable Machine (Worst or best team name ever? You decide.). This returns us to more familiar grounds as Penny Akk has started her superhero training and is trying to figure out a way to gently break it to her parents she's been committing petty crimes across the solar system. Yes, I said solar system if you haven't read Please Don't Tell My Parents I Blew Up The Moon.
Much of the book relates to Penny dealing with the fallout of the second novel as Remmy, a middle school steampunk mad scientist from Jupiter (long story), wishes to gain revenge on our heroine. Penny finds the whole thing ridiculous as Remmy is a fundamentally decent person operating from bad information.
As such, it's actually Remmy who is in more danger as the young girl threatens to expose Penny's secret identity to the world. That's a crime punishable by death according to Los Angeles' quirky engagement rules. As such, Penny is doing her darnedest to keep her nemesis (friend? Friemesis?) safe until she can convince her to not fight. A large part of what makes the novels so enjoyable is they actually do believe in things like the power of friendship and fun.
Another thing I liked is it's confirmed what we've suspected all along that Penny Akk isn't cut out for superheroism. While she's a lovely child, she enjoys trouble and raising hell way too much to be the kind of person who sets out every night to fight crime. Given supervillains are, with rare exceptions, mostly harmless in Los Angeles--this is more like choosing Horde or Alliance than anything resembling a moral choice. This is a good thing as Penny is far too lovable as a "bad" guy.
As the protagonists get older, things are starting to become a bit more dangerous for them and the rules more serious. When they were twelve-year-olds, they could get away with murder but now they're facing slightly more dangerous foes. Mammon, from I Did Not Give That Spider Superhuman Intelligence, seems like a joke but he's still a man who had no problem trying to murder children in the previous book. I wouldn't be surprised if the series started taking on a somewhat more Harry Potter-like edge.
The end of the book, for example, has a shocking twist which may be the most dangerous thing to happen to the (anti)heroes yet. Even so, I'm actually going to have to remove a star because the cliffhanger ending required a large number of really bad decisions from our protagonists they're too smart to make. I also think the raised stakes are a bit incongruous to what has mostly been a slice-of-life series so far. In short, the books are so sweet, I actually don't want them to become darker and more dangerous.
In conclusion, if you liked the previous installments of the series you're sure to like this one. The books are full of humor, silly characters, oddball situations, and a focus on friendship. While aimed at younger readers, I've enjoyed the books tremendously as an adult and think you will too. Time will tell if the series takes a dip in enjoyment but it hasn't yet.