Clifford D. Simak was a journalist from Wisconsin who wrote science fiction as a hobby. After graduating from the University of Wisconsin-Madison he worked at a number of newspapers in the midwest before settling down at the Minneapolis Star and Tribune in 1939. His first science fiction story, "World of the Red Sun", appeared in the December 1931 issue of Amazing Stories (Isaac Asimov reprinted the story in his anthology Before the Golden Age). He published four more stories in the next year, then stopped. He published another story in 1935, but it wasn't until John W. Campbell became editor of Astounding Stories in 1938 that Simak began publishing stories regularly. He published four stories that year, three of them in Astounding, and followed that up with his first novel, Cosmic Engineers, which was serialized in Astounding from February to April 1939.
Cosmic Engineers was an example of Doc Smith-style universe-spanning space opera. The story opens with a scientist named Caroline Martin being awakened from a thousand years of suspended animation when a newspaper reporter named Gary Nelson stumbles across her ship in space near Pluto in the year 6948. Nelson and his photographer sidekick Herb Harper are on their way to Pluto to cover the launch of humanity's first faster-than-light ship for their paper, the Evening Rocket. (Yes, they still have newspapers in 6948. Not only that, they still have evening papers in 6948.)
In spite of her state of suspended animation, Martin remained conscious the whole time, and preserved her sanity by pondering the laws of time and space. She also found herself receiving not-quite-comprehensible telepathic messages from an alien race. When Martin and the news guys reach Pluto, they discover that the team working on the FTL ship has been in contact with the same group of aliens. Martin is able to use the Pluto team's equipment to communicate with the aliens, who live at the edge of the universe and call themselves the Cosmic Engineers. They tell her that the universe is in imminent danger of being destroyed, and that they desperately want help from humanity. The Cosmic Engineers instruct the Pluto team on how to build a hyperspace thingie that will let them travel instantaneously to their world at the edge of the universe. The Pluto team does so, and Martin, the news guys, and two members of the Pluto team travel to the CE world.
They meet the CEs, a mechanical race living in a huge, nearly-deserted city. The CEs tell them that the universe is on the verge of coming into physical contact with another universe, which will result in an influx of energy destroying both universes. To avert the catastrophe, Nelson and Martin must travel millions of years into a possible future and make contact with the descendants of the human race.
In 1950 Gnome Press published Cosmic Engineers as a novel, and Simak took the opportunity to revise and expand it slightly. Paperback Library published a paperback edition in December 1964, followed by at least two reprints (the copy I'm reading is a second reprint from June 1969). The novel was also published in the UK in hardcover and paperback in the 1980s.
Cosmic Engineers has several notable features. First is the obvious Mary-Sue nature of the protagonist, Gary Nelson, like Simak himself a newspaper reporter. Second is Caroline Martin; she is not a simple damsel in distress character, whose only function in the plot is to be placed in danger and thus motivate the hero into being heroic. Martin is an accomplished scientist, and by far the most intelligent of the novel's human characters. It is due to her that the group on Pluto is able to communicate with the Cosmic Engineers, and is able to travel to the edge of the universe to meet them.
Finally, for all its universe-spanning scope, Simak keeps the science in Cosmic Engineers on a remarkably firm footing. The threat to the universe comes from the extra mass that will result from the influx of energy; with the added mass, the universe will no longer continue expanding, but instead will quickly contract back into a primordial cosmic egg, and will have to go through the Big Bang all over again.
Cosmic Engineers is an unusual novel with an interesting cast of characters. At 159 pages, it's a fast read, and the cosmic scope provides the sense of wonder that is the hallmark of good science fiction.