Sixteen-year-old ARIANNA has spent the last ten years trying to fit in and all she wants is for ERIC to kiss her. Tonight at IZZY’s party would be the perfect opportunity… if only the six-year-old version of herself hadn’t suddenly appeared, accidentally time-traveling into Arianna’s reality. Arianna is horrified to meet her past self; how could she ever have been so ridiculous? MUP, as she used to be called, is muddy and dinosaur-obsessed and is now ruining Arianna’s life.
To make matters worse, Arianna must accompany her botanist DAD on a voyage to Africa in search of a cure for a looming environmental disaster: the black dread, a deadly pathogen that is threatening the world’s plants. But Mup, intent on seeing the wild places, stows away on their trip and causes havoc with her dinosaur obsession and carefree ways.
Upon arrival in Africa, they encounter the evil MR. LEOPOLD who is also racing toward the Forgotten Forest in search of riches. Fortunately, Arianna and her dad meet a clever local girl, WAASI, who helps them locate the Forgotten Forest, which may hold the clue to the remedy they’re searching for.
Working together, Arianna and Mup find the Forgotten Forest and guarding it, the legendary beast Mokele-mbembe. They outsmart Leopold and his army and find the cure to the black dread. Along the way they learn to love and accept themselves just the way they are. Mup learns that becoming a teenager is not so bad, and Arianna embraces her spirited, authentic, imperfect self.
At last after sending her younger self back into her own time, Arianna is proud to call herself Mup and be the person she was meant to be all along.