Doctor M - Dark Angel IV

A child left by her mother at a restaurant in a department store has Fumiwako's contact information and a picture of Tatsuki, an old acquaintance of Fumiwako's.... Where did the mother go?　Why did she entrust the child to Chiwako? And what is the relationship between the child and Tatsuki? Fumiwako becomes the guardian of the child, Rio, and travels around the country in search of clues...!