This is the series' only two-part serial.
Ophelia Frump, nutty, strewing flower petals, forever jumping into fountains and brooks, is based on the same-named heroine from William Shakespeare's Hamlet. Shakespeare's Ophelia goes mad, has a monologue about flowers, and drowns in a stream. The design of Ophelia Frump appears to be based specifically on Jean Simmons' performance of Ophelia in Hamlet (1948), as opposed to any other production of the same play.
The main story takes place in 1952, with the frame story taking place in 1965.
This episode and its follow-up confirm that Grandmama comes from Gomez' side of the family, given the presence of Granny Frump. She's played by Margaret Hamilton, who was no doubt cast because of her iconic role as the Wicked Witch of the West in the classic MGM version of "The Wizard of Oz."