Task: Question Answering
Input (English): Passage: Seeking background material for a mystery he is working on, novelist Charles Condomine invites eccentric medium Madame Arcati to his home in Lympne, Kent, to conduct a séance. As Charles, his wife Ruth and their guests, George and Violet Bradman barely restrain themselves from laughing, Madame Arcati performs peculiar rituals and finally goes into a trance. Charles then hears the voice of his dead first wife, Elvira. When he discovers that the others cannot hear her, he passes off his odd behaviour as a joke. When Arcati recovers, she is certain that something extraordinary has occurred, but everyone denies it.
After Madame Arcati and the Bradmans have left, Charles is unable to convince Ruth that he was not joking. After Ruth retires for the night, Elvira becomes visible, but only to Charles. He becomes both dismayed and amused by the situation. Relations between Charles and Ruth become strained until he persuades Elvira to act as a poltergeist and transport a vase and a chair in front of his current wife.
Ruth seeks Madame Arcati's help in sending Elvira back where she came from, but the medium professes that she does not know how. Ruth warns her disbelieving husband that Elvira is seeking to be reunited with him by arranging his demise. However, the spirit miscalculates; Ruth, not Charles, drives off in the car she has tampered with and ends up dead. A vengeful Ruth, now in spirit form, harasses Elvira to the point that she wants to leave.
In desperation, Charles seeks Madame Arcati's help. Various incantations fail, until Arcati realises that it was the Condomines' maid Edith who summoned Elvira. Arcati appears to succeed in sending the spirits away, but it soon becomes clear that both have remained. Acting on Madame Arcati's suggestion, Charles sets out on a long vacation. However, he has a fatal accident as he is driving away, and he joins Elvira and Ruth as a spirit. 
Question: What causes Charles to be reunited with his dead wives?
Output (English): a fatal accident.