Peterborough, who, in spite of his perverted notions of honor, would not on any account have passed the river before the time stipulated, heard the neighing of horses in the town and supposed that some of the troops were leaving it.

In order, therefore, to create suspicion and confusion among the enemy, he ordered a body of men near the river to fire straggling shots as if small parties were engaged at the outposts.
Mahony hearing these sounds sent word that whatever collision might have occurred it was the result of no breach of the terms of capitulation on his part, and that, depending implicitly on the honor of an English general, he could not believe that any foul play could take place.
Peterborough sent back his compliments by the officer who brought the message, with expressions of gratification at the good understanding which prevailed between them, and at the same time he proposed that Mahony, for the security of the inhabitants of Murviedro, and to prevent his troops being molested as they retired from the town, should permit a regiment of English dragoons to cross the river and to form a guard at the gates, offering at the same time to deliver up a number of his officers as hostages to the Spanish for the loyal fulfillment of the terms.
In an evil hour for himself Mahony consented to the proposal.

When the Spaniards saw Peterborough's dragoons advancing without opposition through the difficult pass, and up to the very gates of the town, their suspicions of the treachery of their leader became a certainty.

The Spanish officers each got his company or troop together as quickly as possible and hurried across the plain to the camp of the duke, where they spread a vague but general panic.

The officers accused Mahony of treachery to the Spanish general, and the national jealousy of foreigners made their tale easily believed; but Peterborough had taken another step to secure the success of his diabolical plan against the honor of his wife's relative.
He made choice of two Irish dragoons, and persuaded them by bribes and promises of promotion to undertake the dangerous part of false deserters, and to tell the tale with which he furnished them.