Two thieves started a fire in the garden of an 86-year-old woman's house in order to steal her purse.
The man and woman knocked on the door of their victim in Strathy Close, Whitley in Reading, saying they needed a bucket of water.
While she went to get the water on Tuesday they entered her living room and stole her purse, containing a large amount of cash.
The woman found there had been a small fire by her shed which had gone out.
Ch Insp Jim Weems said: "This is an unusual type of distraction burglary, but it is particularly worrying that the offenders went to the lengths of starting a fire in an attempt to support their story.
"Distraction burglaries are normally targeted against the elderly and vulnerable and the level of shock and upset they cause can be devastating."
Police said the woman could only give limited descriptions of the offenders, with the woman being white, in her fifties and that she spoke with a local accent.
She was wearing a hood over her head. The man is white.