It's nighttime. Marco, in his little bed, thinks about his drawing. In the foreground he has painted a little mermaid, and in the background Venice, lying under the sea.

Suddenly, someone knocks on the window. It's a little mermaid, and she says to Marco: "Thank you for putting me in your picture! But you've never seen Venice at the bottom of the sea... I've come to take you to see it!" Marco is amazed... behind the window is the sea, and he can see seaweed and little fish! "Put on this diving suit and these fins and this mask," says the little mermaid, "so you'll swim more easily!"