Which preposition to use with understrapper

at Occurrences 1%

Beatrice's father, who had talked to him, had probably committed the crime: if not he, one of his understrappers at his order.

of Occurrences 1%

Under their roof no harm should ever befal me; and, even if the understrappers of the law should discover my retreat, they would to a man die in my defence, sooner than a hair of my head should be hurt.

Which preposition to use with  understrapper