Son: Dad, is there really a ghost in this world? Dad: No, son. What's the matter? Son: Our nanny says there are ghosts in this world.

First of all, dad's words are inconsistent. Since he said that there are no ghosts in the world, he should not want to pack up and leave after listening to his son's words, but to see who is babysitting with a meridian beard or calling the police (because if he doesn't believe in ghosts, he will definitely suspect that he is a thief or something). Since dad wants to leave, he may know that there is such a nanny, and this nanny is dead, and this nanny's death must be related to this father, otherwise he will not want to run away.

Moreover, the nanny listened to this son's words, and the nanny was lost in thought for a while, which proved that she was thinking. Then she said that dad died four years ago, so according to the answers of dad and nanny, it can be concluded that dad and nanny absolutely knew each other and had an unspeakable relationship.

Thirdly, about passers-by, first of all, passers-by said that this house has been unoccupied for five years, which proves that this passerby has been passing outside this house for five years, and no one will pass in front of a house for five years without interruption, so this passerby must have something to do with this family.

To sum up the above three points: First of all, dad must have hired a nanny, but there may be an argument with the nanny for some unknown reasons. Then maybe dad is determined to kill the nanny, and the nanny may kill dad to protect himself, so dad and nanny may die together. Passers-by may be the housekeeper or a servant of this family. He heard the noise, went into the room, saw that the master and nanny were both dead, and fell down the stairs in panic and died. So only my son is not a ghost.

However, the contradiction of these inferences lies in time. The nanny said that my father died four years ago, and passers-by said that no one lived for five years. In the narration of passers-by, it is judged that the owner died for five years, and in the narration of the nanny, it is judged that the owner died for four years. How did the 1 year time difference come about? I think this is the crux of the problem.

If it is determined that only one person is a ghost, it can only be the father according to the time point. First of all, maybe this so-called nanny is not a nanny, but the hostess of this family. Then why did she tell her son that she was a nanny? Then she may be hiding her identity. Why would she hide her identity? Could be life-threatening. It can be inferred that this family of three moved away from here five years ago, establishing that passers-by were uninhabited for five years. Then why do you hear voices now, proving that this family has come back? Maybe only the nanny (mistress) and the ghost of my son's father have come back? Why is it the ghost of father? From the above nanny's trance and answer, we can know that my father died four years ago, and his death must be related to the nanny (mistress), so. That's why this nanny may be the hostess, because she wants to hide her identity as a murderer, but she has to take care of her son, so she has to move back to where she lives now and change her identity.