Little tadpole Dou Dou has never seen his mother since birth. Seeing everyone else with their mothers, Dou Dou feels extremely envious. He then goes to ask the village chief, who tells him that his mother is trapped by a large net upstream in the river!

Determined to find his mother, Dou Dou sets off on his journey. The village chief warns him that traveling upstream requires passing through the dangerous rocky forest at the bottom of the river and the terrifying Black River Valley!

Despite the danger, Dou Dou, along with his good friends Xiao Xiao and Bei Bei, are determined to help him. So, they set off together! Welcome to the fantastic world of the dark underwater, and join Dou Dou on his journey to find his family!