here is the answer:
John Hallock is the protagonist of the story "A Shady Plot". He is the husband of Lavinia an is plagued by the ghost of Helen. Helen tells John to prevent the use of Ouija Boards, if he wishes to continue his successful career as a ghost story writer. John comes across as a plagued husband, who is worried about his wife's reaction on perceiving an actual ghost. He loves his wife in spite of the fact that she is a spendthrift.  Lavinia is the quintessential modern wife, who loves to spend money and indulge new fashions or trends. She is the one who purchases an Ouija Board and organizes the Ouija party. She may come across as a vacuous wife, but finally displays genuine love and affection for her husband.

here is the another answer which u feels better u can read
The ghost Helen;- Helen the ghost is a lady ghost in the shady plot. helen in her early part of life was a writer. she with her other friend ghost open up 'the writers' inspiration bureau' to help the upcoming writers who faced problems in writing stories. she and her friends were exhausted of the ouija board were she and her friends on a strike.
Mr.John Hallock;- john was an upcoming writer. He used to write ghost stories especially for the jenkins publishing house. Every time John would sat to write a ghost story he would start thinking deeply but didn't  have any ideas but at last end up writing a good horror story.john was a very caring husband for Lavinia.