Hail Hydra? More like Fail...Hydra...never mind.

So Captain America, much to my chagrin, has been announced as a secret Hydra agent. Not only do I find this completely ludicrous, I also find it very confusing. I don't really read recent comics with only a few exceptions and I really don't follow anything involving/following Secret Wars. Can anyone explain to me how Captain America, who literally punched Hitler in the face, could have been working for Hydra the whole time?