Unsure of this sentence; lack of verb is throwing me off here


I can't properly understand this sentence

> そして, そのマントは 他人には決して見えないことを, 彼女たちは知っていた.

I think it means:

And the girls knew, those cloaks (would reveal/showed) to strangers something
they've never seen? And those cloaks (showed) something to strangers the girls
knew they've never seen?

I want to understand this thoroughly. The lack of any verb in the first phrase
is really throwing me off.




マントは見えない : The cloak is invisible.

Probably, this resolves your problem.

Overall, "And, they knew that the cloak was definitely invisible to others."

