Uhura's Song (Star Trek S.)

Eaiou is a planet where catpeople live. They start getting ill and die. Humans are being infected too. Dr. Mc. Coy has his hands in his hair. Uhura has a friend who taught her some "forbidden songs". She tell Spock that the Eaiouans are not from the planet. They travelled to Eaiou many centuries ago. Spock and Uhura start using the songs to find the homeworld. Maybe there will be a cure there....