One morning, Boubou wakes up struck by the clarity of his feelings for Nadia. He grabs a sheet of paper, hurriedly writes the words "I knew it!" and entrusts his rat, Fromage, to deliver the letter to her. But when Nadia discovers the message, she is not sure she understands... Their correspondence leads to a misunderstanding and then a tangle, and when both start sulking, Fromage decides to take matters into his own hands... The epistolary exchange between the two children illustrates the difficulty of putting feelings into words and the limitations of language in the face of love.