I will reply to this as best I can, to the best of my knowledge.
Evil is all that is apart from God. Like Severus relates, evil in uncreated nothingness - it is not a thing, it is nothing. Now this is hard to comprehend especially because we refer to it as a noun as if it had substance, but as "love" is a noun that cannot be quantified, we must do so also with evil as the opposite of love. It is also hard to comprehend because we think of it as spacial, where one can be eternally damned, and this is where we are limited because it is ultimately beyond our capability to understand.
Evil is the darkness in which we have all been born, and Christ is the light that shines in the darkness. Just as darkness is the absence of light and has no substance, evil is the absence of good and it too has no substance. When light shines in darkness the darkness has no power to overcome it because light alone has substance. We are born in darkness and God calls us to his goodness (the light) but he does not force us. Just as we cannot see in the dark, we also cannot see in this world and we continually fall into sin, but Christ is the light shining in darkness and those who choose to follow him are given sight in the darkness from the light that shines from him, and we are then able to see our follies. We do not see this light entirely and are incapable of approaching it on our own accord, but we must be called because the darkness cannot comprehend the light.
Evil has no power over us unless we submit to it. If we then adhere to Christ then He will shine His light for us which destroys the darkness. At the final judgement, those who are cast away into the lake of fire will remain in darkness forever, for God will no longer visit the darkness to claim back His creation. When visited the darkness He formed for Himself human flesh consubstantial to our own, trapped in darkness, and returned to Heaven with that flesh, securing once and for all that flesh can be saved from darkness. So then, when we adhere to Christ at our judgement we are made God (theopoiesis) and sons by adoption and are able to leave the darkness forever because of the special quality that is transmitted to us through marriage to the Son - Christ is the bridegroom, the church is the bride. This union may be likened unto the union of a magnet and a piece of steel, whereas Christ is the magnet and the steel are believers, when the steel unites with the magnet it becomes itself a like magnet but derives all its magnetic properties from the magnet and when separated loses all those qualities.
Glory be to God for ever.