Neither Mapp nor Lucia win a seat at the local election and, for Mapp, who would appear to be pregnant, things are looking bad as she and Benjy have lost their investment in the Siriami mine and are strapped for cash. To help out - superficially - Lucia proposes that they swap houses, which they do and Lucia is excited when she believes that she has discovered Roman artifacts buried at Mallards. In the event they turn out to be modern trinkets but, so as not to lose face, Lucia holds a garden party, where it is also discovered that Mapp's presumed pregnancy is ...