From author James Blish, this is "Spock Must Die!", a Star Trek novel in paperback format, published in 1970. This copy is in very good condition; there is a white partial crease line on the front cover and light signs of wear on edges and corners.
The book has 118 pages. It weighs 2.5 ounces and measures 7 in x 4.5 in x 0.5 in.