Nanu and Otto are off on a climbing adventure – to the top of Lion Mountain! Otto is a born explorer, just like his grandma, who is brave and bold and can’t resist the urge for adventure. But Nanu is having a forgetting day. She forgets her backpack and the name of the mountain … and then she forgets the way home and leads them deep into the forest. Can Otto remember all the things Nanu taught him about being a great elephant explorer and guide the expedition home?