The first act of the opera may be looked upon as an induction to the conventional comedy which comes to an unconventional and tragic end through the fact that the Clown (Canio) is in real life the husband of Columbine (Nedda) and is murderously jealous of her; wherefore, forgetting himself in a mad rage, he kills her and her lover in the midst of the mimic scene.
The lover, however, is not the Harlequin of the comedy, but one of the spectators whom Canio had vainly sought to identify, but who is unconsciously betrayed by his mistress in her death agony.

The Taddeo of the comedy is the clown of the company, who in real life entertains a passion for Nedda, which is repulsed, whereupon he also carries his part into actuality and betrays Nedda's secret to Canio.

It is in the ingenious interweaving of these threads--the weft of reality with the warp of simulation--that the chief dramatic value of Leoncavallo's opera lies.
Actual murder by a man while apparently playing a part in a drama is older as a dramatic motif than "Pagliacci," and Leoncavallo's employment of it gave rise to an interesting controversy and a still more interesting revelation in the early days of the opera.

Old theatre-goers in England and America remember the device as it was employed in Dennery's "Paillaisse," known on the English stage as "Belphegor, the Mountebank." In 1874 Paul Ferrier produced a play entitled "Tabarin," in which Coquelin appeared at the Theatre Francais.
Thirteen years later Catulle Mendes brought out another play called "La Femme de Tabarin," for which Chabrier wrote the incidental music.

The critics were prompt in charging Mendes with having plagiarized Ferrier, and the former defended himself on the ground that the incident which he had employed, of actual murder in a dramatic performance, was historical and had often been used.