Nice pictures, by the way. They really help show the problem. With this much webbing and visible mite presence, it is likely that the mites were there a long time, possibly for months. Spider mites can hang aroung undetected for weeks, especially when house temperatures are relatively cool. Once they multiply a bit, it seems they explode overnight. Where did they come from? Usually they come indoors in the fall. If the plant was brought indoors, they probably were on it all along. If you have other plants, it would be good to check them for infestation too. What to do? It takes some persistence on your part - insecticidal soap helps but can take awhile to get results. You can speed the recovery by giving the plant a gentle shower (emphasizing gentle) in the sink or bathtub - this type of physical removal makes a big dent in the population. You can't really fix the damaged leaves, but the plant should perk up with some new leaves.