Notorious logical figure having change of heart? Just a bit (5)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

SP [o] CK (notorious logical figure = part-alien character in the Star Trek series, known for thinking logically rather than emotionally) with the middle letter (heart) changed. I’m not sure it’s quite fair to do this without saying what the letter changes to , but in this case it’s not too hard to work out. As in “not a speck of dirt” = a tiny bit.