Star Trek: The Original Series+2
The Great Puzzle or The
by solomonara
During a routine science mission on a frozen planet, Spock suddenly finds himself in something of a hairy situation. Kirk and the crew scramble to understand the cause of Spock's sudden leporine predicament - before it's too late and the Enterprise is down one first officer (and up one fuzzy mascot). Less crackfic than you might expect, I've been told. Also, as has been suggested on more than one occasion, possibly worth reading just for the chapter titles.