Cicero on Treachery

No treachery is more insidious than that which is hidden under a pretence of loyalty, or under the name of kinship. For against an open adversary you could be on your guard and thus easily avoid him; but this hidden evil, within the house and family, not only arises before you are aware but even overwhelms you before you can catch sight of it and investigate it.

Cicero, In Verr., 2.1.13