The Knight in Tights (Witch Knight, Inc.) by T.W. Kirchner

Chivalry isn’t dead—it’s online. A stroke of luck for Chartreuse Theodore, whose Potion and Spell Deficit Disorder routinely creates catastrophes for the young witch. This time, she magically misplaces her coven’s priceless spell book, and if an evil sorcerer bent on destroying her coven reaches it first, Char may lose more than her magic. Expecting wicked witches, gremlins, and vengeful spirits, Char summons a wizard knight for protection—or so she believes. Lance Stone is a computer wizard, not skilled in magic but agrees to the task because he thinks Char holds a clue to finding his long-lost father. As danger closes in, Char’s only option is to face the powerful sorcerer, sacrificing herself to save her coven. Although there’s no amount of coding Lance can do to solve the crisis, he has a hidden resource that may shut down the sorcerer if time doesn’t run out first. Their road is rough and twisty, but the duo’s ancestral destiny pushes their paths and their hearts in the same direction.