Inspector Wexford: An Unwanted Woman – A Riveting Mystery in Kingsmarkham

From the VHS cover:
Among the senior citizens of quiet Kingsmarkham, these apple-faced kindly country folk, the world of passion and desires is not yet dim. Did septuagenarians Mr. and Mrs. Betts murder their unbearable old mother Ivy Wrangton, to inherit her house? Gossip among the Castle Road post office ladies says that when Mrs. Wrangton 'died' there would be no inquest; yet Elsie Parrish, Mrs. Wrangton's best friend, who also got a little something in her will, won't hear of any foul play.
The Case at first seems as innocuous as the suicide of childless Ann Waterton, an old lady befriended by lonely mixed-up teenager, Sophie Grant.
What can be the dark side of this sweet story?