Okay, I was wrong when I listed the best of Season 1 and left this off the list. This is clearly one of the top episodes of Season 1, which though clearly lower in production value and unspectacular in its villians is still turning out to be one of the better seasons dramatically. The sisters are forced to travel back in time to stop a deal that their mother made with, what?, a warlock, would be my guess, named Nicholas. I don't think he was called a demon at any point, he doesn't look like a demon, and warlocks again are Season 1's thing, so... Nicholas himself is neither especially frightening nor intimidating though he does have a rather sinister power, being able apparently to cause painful death with a turn of his hand.
No, the best part of the episode are the characters of Grams and Patti, played very well throughout the entire series by Jennifer Rhodes and Finola Hughes. Grams especially is fantastic as the snappish, feminist superwitch, who seemingly was more the sisters' mother even before Patti died. Patti herself is more concerned with her daughters' normal lives than their magical ones, being similar to Piper in that way though few others. It is great to see the women work together to get rid of Nicholas and get back to their own time. The young girls as Prue and Piper were cute, of course. Anyone else notice that the young Piper had blue eyes? I guess they changed color at some point. Oh well, minor. Great episode.