Kip and Molly flee Ireland in search of a better life. On the way, they lose their parents. For the sake of food and a roof over their heads, they enlist in the gloomy Windsor estate. All local residents avoid this terrible place. A dilapidated mansion stands in the shadow of a huge ominous tree. And the inhabitants of the estate are always pale and sick. At night, the estate is visited by a distinguished guest in a black hat. He goes around room after room, leaving traces of dirt, and then disappears. Every day, life for the Windsors becomes more and more unbearable. Kip and Molly no longer distinguish reality from nightmares. Perhaps they will find the answer in a secret room that is always locked... or perhaps the secret hidden behind the green door will make them hostages of the house forever.