It was a REALLY REALLY long Spander, and I think Spike gets amnesia or something, from stepping in a puddle before being electrocuted pretty badly from what I recall, and when he wakes up he's.... well pathetic really. And not Spike. So Xander nurses him back to health and I think there may be something about Spike becoming completely docile when called William, but that could be from another fic.
FOUND!! Thankyou emelye_miller!!
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