A complicated story which is narrated at length in the course of the play explains the peculiar laws of Arcadia on which the plot hinges[186].  These comprise an edict of Diana to the effect that any nymph found guilty of a breach of faith shall suffer death at the altar unless some one offers to die in her place; likewise a custom whereby a nymph between fifteen and twenty years of age is annually sacrificed to the goddess.  When besought to release the land from this tribute Diana through her oracle replies: 

    Non avra prima fin quel che v’ offende,
    Che duo semi del ciel congiunga amore;
    E di donna infedel l’ antico errore
    L’ alta pieta d’ un pastor fido ammende.

The only two in Arcadia who fulfil the conditions of the oracle are Silvio, the son of the high priest Montano, and Amarilli, daughter of Titiro, who have in their veins the blood of Hercules and Pan.  These two have consequently been betrothed and, being now arrived at marriageable age, their final union is imminent.

At this point the play opens.  Silvio cares for nothing but the chase, regardless alike of his destined bride and of the love borne him by the nymph Dorinda; Amarilli is seemingly heart-whole, but secretly loves her suitor Mirtillo, a stranger in Arcadia, whom, however, she persists in treating with coldness in view of the penalty involved by a breach of faith.  Mirtillo in his turn is loved by Corisca, a wanton nymph who has learned the arts of the city, and who is pursued both by Coridone, to whom she is formally engaged, but whom she neglects, and by a satyr.  Almost every character is provided with a confidant:  Silvio has Linco; Mirtillo, Ergasto; Dorinda, Lupino; Carino[187], the supposed father of Mirtillo, has Uranio; Montano and Titiro act as confidants to one another.  The only case arguing any dramatic feeling is that in which Amarilli makes a confidant of her rival Corisca; while Corisca and the satyr alone among the more important characters are left to address the audience directly.  Even the confidants sometimes need confidants in their turn, these being supplied by a conveniently ubiquitous chorus.

In the first scene of Act I, after the prologue, in which Alfeo rises to pay compliments to Carlo Emanuele and his bride, we are introduced to Silvio and Linco, who are about to start in pursuit of a savage boar which has been devastating the country.  Linco taxes his companion with his neglect of the softer joys of love, to which Silvio replies with long-drawn praise of the free life of the woods.  The scene is parallel to the first of the Aminta, and the author has sought here and elsewhere to point the contrast.  Thus where Tasso wrote: 

    Cangia, cangia consiglio,
    Pazzerella che sei;
    Che il pentirsi dassezzo nulla giova;

Guarini has: 

    Lascia, lascia le selve,
    Folle garzon, lascia le fere, ed ama.