I'm interested in covers of modular curves (especially cyclic covers) and I'm sure there's a lot of information out there available on this topic. However, I'm unable to locate any literature (on Google or MathSciNet). Anyone has any references?

Edit: In response to the comment below, I'm particularly interested in the local properties of the cover. For example, how, if at all, Heegner points or supersingular points, translate into properties of the fibers over these points.