Ben and Pearl are back at Dr Woo's, eager to spend another day working with imaginary creatures!When Mr Tabby directs them to the roof, they finally have a chance to meet the reclusive dragon that's been hiding out at the hospital - and that Ben and Pearl had spotted flying over Buttonville on Ben's first day in town. But all too soon, they're summoned to the basement, to the hospital's portal into the Imaginary World. A call for help has come in, and with Dr Woo away, Ben and Pearl are the only ones who can respond.Their mission: to rescue the rain dragon and uncover the identity of a poacher who's found a way to enter the Imaginary World. What does this mean for Dr Woo and her mythical creatures? Only time will tell. Luckily, Ben and Pearl are up for the challenge!