Kate McKinnon Is Ready for the 'Adventures to Continue' in Sequel to Bestselling Children's Mystery Novel — See the Cover! (Exclusive)

Kate McKinnon has a message for the young readers of her bestselling novel: "It's not over, you guys!"

In an exclusive with PEOPLE, the Saturday Night Live alum and author of The Millicent Quibb School of Etiquette for Young Ladies of Mad Science is revealing the cover of the book's forthcoming sequel, Secrets of the Purple Pearl.

The mystery novel, expected to arrive this fall, marks another installment in her New York Times bestselling series, which she kicked off in 2024.

As McKinnon, 41, explains, sharing the stories of the Porch sisters and their mentor Millicent Quibb has been "one of the great honors of my life."

"I was so inspired by the future mad scientists that I connected with through writing this book, and I can't wait for the adventures to continue," McKinnon tells PEOPLE. "It's not over, you guys! The KRA is still out there, so hop in the Gerbilcar and buckle up!”

For those outside of the series' 8-12 readership range, the books follow the adventures of Gertrude, Eugenia and Dee-Dee Porch in the snooty town of Antiquarium. The new installment takes place at the Purple Pearl Hotel where "everyone," including the "nefarious group of evil mad scientists, the Krenetics Research Association" has taken off to, per the synopsis.

While attempting to "resurrect" their leader Talon Sharktüth, the mad scientists are also "hot on the trail of the legendary Purple Pearl, a source of power that is rumored to be lost at the bottom of Kagloopy Lake." To do so, they have to find the "mysterious creature called a Shrimpmaid, boil the lake (and everything in it) away and pluck up the pearl." Of course, unless Millicent, Gertrude, Eugenia and Dee-Dee have something to say about it.

"They are determined to stop the KRA, even though they are now full pariahs in Antiquarium society," a synopsis reads. "While Millicent and the gang work together to prevent the second coming of Talon Sharktüth, they discover more secrets than they bargained for — including where they came from, and who they truly are… It’s a mad science summer vacation they’ll never forget!"

For its cover, Secrets of the Purple Pearl gives readers a look at one of the creatures that the Porch sisters encounter on their latest journey around the lakeside hotel.

McKinnon previously called the first book in the series, which hit shelves back in October, a "story about maintaining hope in the darkest times." As she detailed, she rewrote the book roughly 500 times over the course of 12 years.

"I think this genre allows for such true humor and this wonderful blend of silliness and heart that is just how I feel about and experience the world," she said. "And so it's just suited to me and my goals, my ends."

"That's childhood: feeling weird, trying to understand that everyone has something weird about them," the comedian and author added. "I mean, when I was 12, I was in flannel and I had a perm, and I had a space between my teeth so large that people often asked me if I had lost a tooth. I had a pet iguana, and I was just so weird... I had some adults in my life who kept on encouraging me to be what I was, my parents chief among them. And I think that a young person needs those kind of people and then to nurture their gifts. And then when they are adults, they have a responsibility to pay it forward. And I guess that's what I'm trying to do."

Secrets of the Purple Pearl is now available for preorder ahead of its Sept. 30 release via Little, Brown Books for Young Readers.