Knock at your own risk! Lukasz doesn't know what's happening to him: Suddenly a woman shows up at his house claiming to be his aunt. And because Lukasz's mother is in the hospital, the stranger takes him along without further ado. And so Lukasz ends up in her small, rather run-down boarding house in the country. He is not entirely comfortable with the whole thing. And his suspicions are not deceiving: when he discovers the blue door on his wanderings through the boarding house and finds out what's behind it, Lukasz ends up in the biggest adventure of his life ....