Vulcan! (1978) is a science fiction novel by American writer Kathleen Sky, a tie-in of '. The book is an adaptation of an unproduced spec script by Sky.
Kathleen Sky submitted a spec script to the producers during the production the show's . She was informed the script might be produced the following season. However, the series was cancelled late in the third season's production.
Editors at Bantam Books recruited Sky to contribute a Star Trek tie-in novel sometime after 1976. She opted to adapt her unproduced script. David Gerrold, the writer of the episode "The Trouble with Tribbles", wrote a foreword to the novel. Sky's husband, Stephen Goldin, also wrote the tie-in novel Trek to Madworld, also published by Bantam.
As of 2008, a first edition copy of Vulcan! was valued up to .
Ion storms have caused the boundaries of the Neutral Zone between the Federation and Romulans to shift. The planet Arachne IV, inhabited by a strange ant-like race, could be lost to the Federation due to the changes in space. However, Mr. Spock goes on a death-defying assignment into a war of ant-like creatures along with a scientist who dislikes Vulcans.
A bibliographic note in the December 1979 edition of Science Fiction and Fantasy Book Review explained that "Sky ascribes more emotion to Spock than is logical under the circumstances [of the plot]".