In the novel Mrs McGinty's Dead, Cullavon is a town three miles from Broadhinny. Mrs McGinty's niece lives in Cullavon with her husband.
On the night of Mrs Upward's murder Edna had told her father that she was going to the pictures in Cullavon, with Reg. There is a bus service between the two towns.
The Lamb is an inn in Cullavon. Superintendent Spence suggested to Poirot that he could stay there, since The Three Ducks in Broadhinny doesn't put people up.