In a fictional backstory created by the H. P. Lovecraft Historical Society, A Shoggoth on the Roof was originally attempted by The Other Gods Theatre Company in 1979 in Los Angeles.
As a result, attempts to stage A Shoggoth on the Roof are open to legal challenges and hence rare.
The action opens in a manner reminiscent of Fiddler, with a shoggoth on the roof of the Miskatonic library building.
("Tentacles") Back at Armitage's house, his three daughters, Prudence, Asenath and Jill, along with their mother Marion, are cleaning.
The three daughters begin chatting and Prudence reveals that she has fallen in love with Herbert West, a doctor and assistant professor at the university.
The action then moves to a graveyard, where Randolph Carter and Harley Warren are discussing how best to enter an ancient tomb.
In a scene that appears to take place a few days later, Jill and Asenath attend a ceremony at the Esoteric Order of Dagon.
("Shoggoth Prayer") Asenath seems attracted to the cultist, and asks Jill to follow her down to the beach to watch him.
Jill, however, decides to stay, and watches Obed Marsh, a decrepit old man, clean up the hall.
Carter and Warren fight them off, but Armitage is still worried about how to break the news of Herbert and Prudence's marriage to his wife.
Obed Marsh and Jill ask Armitage for his blessing for them to marry, explaining that they have fallen in love.
("Arkham, Dunwich - second reprise") The song is interrupted by Wilbur Whateley, who is enraged at both being denied Prudence and at not being invited to the wedding.
He vows revenge, and reads an incantation from the Necronomicon to summon Cthulhu, who appears behind the library and crushes many of the villagers.
The musical was staged for the first time, in a Swedish translation, at Miskatonicon, an H. P. Lovecraft convention in Sweden, on November 4, 2005.