[Elsie]

Everything that happens happens either because God willed it to be so, or because God chose to permit it to be so. That's pretty basic.

So is this:

[Campion]

The devil can't do anything that God doesn't permit him to do. No exceptions.

Manichaeanism is essentially the heresy that God and the devil are equals, a "good god" versus a "bad god". Christians aren't Manichees.

Not only can the devil only do what God permits him to do, but the devil's very existence is sustained by God moment-to-moment. (As is the existence of every other creature, which is, after all, is what the devil is.)

So why does God permit all of this? The short answer is, "Ask him yourself, when you get to heaven!".