"The Stolen Sun" is a 1967 science-fiction novel by Emil Petaja, and is the third in a series of four books based on The Kalevala. It was published as one half of an Ace Double, the other side being "The Ship from Atlantis". Emil Petaja had two different series of books, published across Ace Doubles, this Kalevala cycle being one, and the "Green Planet" series being the other.
Sometime in the intermediate future, Wayne Panu is the pilot of a telepathically linked, sentient ship on a mission to eradicate life. Humanity is reproducing too fast, and that means destroying and colonizing alien worlds as fast as is possible. If you think this is a grim way to start out a book and introduce our protagonist, I agree, and so does that protagonist. Along with his mission of genocide, Wayne starts feeling something else: strange voices in his head. About a third of the way through the book, Wayne is transported, (magically?) to ancient, mythic Finland (although it wasn't clear to me whether this was real Finland in the past, or supernatural Finland in an alternate dimension), where he meets the heroes of the Kalevala. But in this time, they are facing a problem: the sun has disappeared. The people are slowly starving, and the ancient witch Louhi is probably responsible. The final section of the book is Wayne, feigning defeat, in her service and trying to find a way to restore the disappeared sun.
Does that sound like a lot for a 136 page book? Because it was. Much like with Petaja's "Doom of the Green Planet" there were ideas that were talked about that were never really developed. The book takes place in two major locations and even genres: a dystopian space opera and a fantasy Finland. The main thing these locales share is their utter grimness, which at least is a nice artistic risk. But in what is a very short novel, the author introduces two major settings and concepts, and connects them only in the last chapter. With Ace Doubles, I often attribute this to the vicissitudes of the editor's knife. But even with that, past a certain point it leads the reader feeling unfulfilled. What is the relationship between the brutalities of population pressure in a science-fiction setting, and the mystical heritage of the Kalevala? I am sure the connection is in there somewhere, but I couldn't easily find it. So my take away from this work, on a Sunday when I want to take a nap is simply this: science-fiction writers can't just have ideas and imaginations, but they have to find a way to connect the dots for slower readers such as myself.