Accomplice liability makes someone guilty of a crime he never committed, so long as he helped or influenced the perpetrator and did so with the required mens rea. Just what that mens rea should be has been contested for more than a century. Here I consider three major approaches and find them all wanting. I propose rejecting their common (but rarely questioned) assumption that what matters is the helper's mental state toward the perpetrator's commission of an offense. I suggest considering instead his stance toward the perpetrator's intention to act: a helper is an accomplice, on this view, if he (a) intends to see to it that the principal form or keep his own plan to commit an offense and (b) does not intend or expect that plan's frustration. This standard better justifies imposing accomplice liability. It more precisely picks out those helpers culpable for the perpetrator's very offense. And this parity of guilt is the best -- perhaps the only good -- basis for imposing the same liability on accomplice and principal, in a system so retribution-driven as to choose to do so at all.