A timid chemist discovers a potion that unleashes his sleazy side.

Eccentric maladroit Prof. Julius Kelp often gets into trouble with the dean of the large university where he teaches chemistry because his experiments frequently result in the demolition of his laboratory. Wishing to impress Stella Purdy, a beautiful student sympathetic to his difficulties, Kelp tries gym exercises and chemical formulas to improve his appearance. He stumbles on to a mixture that transforms him into singer Buddy Love, a swaggering, handsome bully; and in that personality, he tries to make love to Stella, who is alternately repelled and fascinated. Whenever the effect of the potion wears off, however, he must dash to his laboratory lest he change back to Professor Kelp. At the senior prom, where Kelp is ordered to act as chaperon and is also slated to appear as Buddy Love, the formula wears off during Buddy's number, and his personality reverts to that of the professor. Stella realizes that Buddy is really Professor Kelp and confesses that she has always preferred the quiet, sensitive professor to brash Buddy Love. The two make plans to be married.