This is your resident Thomist bringing you a minute from the Bellowing Ox.
Aquinas has a quite reasonable approach to the existence of angels. His foundation is built upon proof that God exists. Once God is accepted as existing, the existence of angels is not difficult to imagine as the perfection of the universe requires it. Basically, there is a hierarchy of being from God down to the lowest material thing.
Take a moment and imagine a triangle in your head. Have a picture of it in your mind’s eye? Now, do the same thing with a 1000 sided figure. Got it? Most likely not. This thought experiment shows the difference between sense and understanding. Having already proved the existence of God, Thomas says that the very fact that the intelligible is above sense proves that angels must exist; the hierarchy of existence requires it.
It’s not so archaic to believe in the existence of angels as modernity tells us. In fact, demonstrable evidence points to it. That said, not everything that happens is caused by spirits. It’s just to say that they can be.