In the novel Sleeping Murder, Foster is the jobbing gardener at Hillside in Dillmouth. Miss Marple observed that, "He comes twice a week, drinks a great many cups of tea, does a lot of talking, and not--so far as I can see--very much work."
Foster only had vague recollections going as far back as the time of Major Halliday. He did however made a contribution to the case. When Gwenda Reed asked him to dig new steps leading down to the lawn at the spot where she thought they should be, Foster was at first reluctant but later did the job with some enthusiasm. Soon enough he found, to his surprise, that there was an old set of steps right. Someone had covered the steps up and planted over them.
BBC's Miss Marple
In the BBC 1987 adaptation of the novel, Foster is portrayed by Jack Watson.
ITV's Agatha Christie's Marple
In the ITV 2006 adaptation of the novel, neither Foster nor the other gardener Manning is featured because the plot elements about the terrace steps being moved and the shredded tennis net are not used. Nor did Gwenda Reed need Foster to confirm whether her father stayed at Hillside. They got this information from the files in Walter Fane's office.
NHK's Anime adaptation
Foster appears in NHK's anime adaptation of Sleeping Murder where he plays the same role as in the original novel. He discovers the steps have been moved and describes the incident of the shredded tennis net (Manning's role in the original). Despite the relatively large speaking part, the voice actor behind the character is not credited.