In the Retter family’s antique house, an ancient painting has been kept for many decades. No one knows how it ended up in the family or whose brush created it. No one, that is, except the last representatives of the line—Christopher and Christina. One day, a man appears on the doorstep, consumed by the desire to buy the mysterious canvas. He is certain that a key is hidden in the painting—one that can open the way to the greatest treasure of a parallel world. But the stranger has no idea that the key has long since been taken out, and that the treasure will be able to be claimed only by the one who truly does not need it.