[JenB]

I don't think that theory works at all. First off, apparently the whole of what remains of the Order thinks Regulus died a coward. Second, even if he did heroically decide to try to thwart Voldemort, it's just not likely he'd ask Lily. She's a couple years older than him, was in a different House at Hogwarts, married his (probably hated) older brother's best friend, and was Muggle-born. Remember how the Blacks, other than Sirius, felt about Muggle-borns.

Also Lily would have left some sort of clue, or told someone else, about something so very important, no?

[phoenixfeather26]

i dont think kreacher had nething to do with the locket horcrux that's very unlikely but not totally out of the question and kreacher is so loyal to his mistress a.k.a sirius's mom that helping regulus to defeat voldermort by stealing the horcrux would be against his character except if regulus ordered him to b/c he cannot disobey an order from a family member of the blacks so that isnt a bad thought