"The Time Twister" is a 1968 science-fiction novel by Emil Petaja. The book is set in the near future of the time, sometime in the 1970s. Like some of Emil Petaja's other works, it references the Kalevala, but it isn't clear whether it exists in the shared universe of Tramontane and The Stolen Sun. It was also published by Dell, and this is the first novel of Petaja's that I read that wasn't an Ace Double.
Dr. Stephen McCord is an anthropologist that just got out of the hospital with a surgical plate in his skull after an injury in a war zone. He received a tape from an old college buddy who went back to his parent's home in Montana. The tape runs out, presenting a mystery, and McCord flies from San Francisco to Missoula, trying to find the tiny logging town of Finnish immigrants living far up in the woods that his friend disappeared in. While there, he discovers a town lost in time, an alien masquerading the Finnish god Ukko, and a sinister hunchback that may be his only hope for survival. The plot isn't entirely new, but I found it a good telling of that plot. The book has few science-fiction trappings, and McCord's visit to a secluded, mysterious town almost gothic. It also helped me personally that I was familiar with bus journeys to small towns in Western Montana.
My first two experiences with Petaja's works, Doom of the Green Planet and The Stolen Sun were mixed, with me thinking he had too many ideas put together too quickly. With Tramontane, I finally understood his flow. This book, as opposed to those, had a much more linear structure, with a journey from the normal world to a world of strangeness, and with a conflict with a villain who, although bizarre, has understandable motivations. This book was short and kept my interest as the plot unfolded, and the fact that it lacked the baroque plots and settings of his other books could be a good thing or a bad thing, depending on the reader.