If you're in the mood for an unusual M/Sk/K threesome, with GOBS of bdsm, spanking, D/s ... the works ... you have to read Ratadder's Those Hot Winter Nights. Especially if you like sub!Alex to TWO doms.
This things needs a Change-Of-Underwear warning!
Here you go --
http://www.fhsarchive.com/stories/Winter.html