The classic of alternate earths!

Ancient, encrusted with legend, supposedly empty, the old mansion on Spindrift Key stood like a dark and lowering wraith. In this classic science fiction novel the New York Times called "a fast-moving adventure, told with engaging humor", reporter Elspeth Marriner's nose for news leads her into a world of trouble. Make that, into worlds of trouble. 

When she and photographer Mack Fraser, the man she loves to hate, are sent to investigate the old mansion in the Hatteras, they never dream that once inside their lives will never be the same. For, the house is a gateway to alternate Earths, watched over by a mysterious group called the Workers, who guard against more advanced civilizations crossing the dimensional barriers to conquer defenseless neighbors. 

From the Workers, Elspeth learns that her and Mack's presence at the house is no accident. They have been personally selected by the Workers for a dangerous assignment. Their unique combination of talents and knowledge are needed to counter a threat that could plunge the entire world into war. 

If Elspeth accepted the assignment, she would have to cross to another world, aided only by her native ingenuity, surmount a succession of plots and counterplots, with death the price of failure. Worse, she would have to work more closely than ever with the detested Mark Fraser. 

"Merwin has created characters that are human. The House of Many Worlds is entertaining and realistic." (San Francisco Chronicle)

"The House of Many Worlds is an exciting story, with a new and highly unusual twist...outstanding for its realistic characters and expert seasoning of thrills and horror." (H. L. Gold, Galaxy Magazine)