Star Trek: Strange New Worlds - The Illyrian Enigma #3

Synopsis

Captain Pike leads the Enterprise to the Illyrian home world, where the Illyrians who have kidnapped Spock have transformed his body to survive the harsh surface conditions and sent him to investigate an ancient Vulcan artifact on the planet. Once on the planet, Spock finds himself transported to the ancient past where he is part of an unrecorded Vulcan visit to Illyria.