Cosmic Engineers by Clifford D. Simak was originally serialized in Astounding Science-Fiction in 1939 and was later revised in 1950 for book publication. It's often mentioned along with Doc Smith's Lensman, Edmond Hamilton's Interplanetary Patrol, and Jack Williamson's Legion of Space as an epic space opera. It's a sweeping cosmic adventure that compares well with those more famous works and differs from them in some interesting ways.
In the year 6948 reporter Gary Nelson and photographer Herb Harper are en route to Pluto in their small ship, The Space Pup (which is propelled by space warping "geosector" engines) to stop hotshot pilot Tommy Evens from taking off for Alpha Centauri in an experimental FTL ship. As the two vector to the scene they spot a strange object. Gary investigates and discovers it's a small, derelict spaceship. Inside is a woman in suspended animation.
After reviving her they discover she's Caroline Martin, who has been in suspended animation for a thousand years. She was a scientist at a time when war was raging between the inner planets and Jupiter. She developed a new weapon, but its use would have endangered the entire solar system. She refused to turn it over to the military and so was branded a traitor and imprisoned in the ship. She contrived the suspended animation equipment, but her mind remained conscious and she nearly went insane. However, she also developed telepathic powers and received messages from vast intelligences outside the galaxy.
The trio resume course for the outpost on Pluto where they discover that Doc Kingsley has been receiving strange messages from beyond the galactic rim. Caroline confirms that these are from the same source as her telepathic communiques. They are messages from beings that call themselves the Cosmic Engineers who are warning of a grave threat to the universe. They transmit plans for a device that will open an FTL portal and urge the humans to join them. When the Earth government gets wind of this they dispatch ships to stop them, but the five make the journey.
They discover that the Engineers are metallic humanoids of vast intelligence. They have assembled aliens from all parts of the galaxy to help avert a natural disaster. Our universe is but one of many, and another is about to collide with it. Both will be destroyed unless some means is found to avert the catastrophe. They are opposed by the Hellhounds, malicious reptilians who want they universe to be destroyed. And so our protagonists much struggle against overwhelming odds with the fate of the universe in their hands.
This is an interesting book for several reasons. The first is that Caroline is the most intelligent and developed character in the book and plays a leading role in the plot, something that was rare for the time. Another is that the characters aren't called upon to fight a galactic war as is usually the case, but to solve a scientific problem. There's also a scene in the book that anticipates both Fredric Brown's later classic "Arena," and the Star Trek episode based upon it. And the idea of universes in collision is surprisingly similar to some aspects of today's cosmological M-Theory.
Even so this is a somewhat crude novel. The writing is patchy, probably a result of both the serial format of the original and the later re-write. Aside from Caroline the characters are sketchy as was typical of most early pulp sf. And while the plot holds together it's comprised of a rather uneven string of incidents.
Cosmic Engineers lives up to the "cosmic" promise of its title, vividly conveying the staggering scope of the inter-universal scale of the story. It's a minor novel, and Simak would go on to write much better works, but it captures the grandeur of the early "scientifiction" in a fairly original way. While mainly a curiosity today, if you're a fan of the pulp space operas then this is one you'll probably enjoy.