The mysterious beauty Tomomi Ishikawa, nicknamed Butterfly, left a suicide note and disappeared without a trace.

Some time later, her writer friend Ben begins to receive letters from her. The butterfly sends him links to a mysterious code, skillfully hidden in her diary, on the computer hard drive, in public places in flower pots, behind statues - and many other places. From the ancient alleys of Paris to the light-filled streets of New York... In search of a solution, the writer moves further and further. And gradually the question begins to torment him: is the Butterfly really dead? Is what she writes true? But if not, then why did she start this game?

The connection between the real and the unreal, between life, fiction, truth, lies and artistic imagination is completely blurred. A strange and fascinating story of the most unusual friendship that can exist in the world.