Spoilers below for the most recent episode of The Flash.
While The Flash still has yet to give Barry a foolproof idea for how to take down The Thinker, the brainy villain has now found himself all alone and no longer aided by his drugged-against-her-will wife Marlize. Thankfully for Central City, there are only a few weeks left until the big Season 4 finale, where Team Flash will presumably emerge victorious in taking down Clifford DeVoe once and for all. And according to the super-short and sweet episode synopsis for "We Are The Flash," the core group won't be alone in their efforts.
That logline is about as basic as it gets, and yet it still lets us know some important things. One: DeVoe is definitely going to live to see the finale. So for anyone having any wild ideas about bidding him farewell a week or two early, I'm sorry to disappoint.
But the second point is obviously the more exciting one, since it will involve an unexpected teaming, which are always a blast in the Arrow-verse. The question, of course, is who this surprise ally is going to be, since there are several different avenues for that line of thinking to go. The most obvious choice at this point would be the empathetic Marlize herself, since she is clearly not behind the Thinker going through with his Enlightenment plan. But she's spent all this time with The Flash & Co. in her targets, so it's hard to just assume that she'll flip over to the good guys so effortlessly.
Another pretty obvious choice for a Team Flash helper is Mystery Girl, who not only seems to know the relevantly intimate details of the group's members, but also proved just recently that she's got the superpowers to keep up with Barry and the others. We do know that her identity will finally be revealed in the finale, which will lay the groundwork to set up Season 5's big bad, and also that Mystery Girl will play a big part in that transition. So it stands to reason she could throw her (non-thinking) hat in the ring for Team Flash, even though there were several times during her appearances that Mystery Girl just did not look very happy to be talking to the show's protagonists.
Alternately, it could be another hero from within the Arrow-verse offering just the right help needed to take The Thinker down. I wouldn't bet on anyone from Arrow, since we've got that Diggle appearance coming soon. But what about Wally from Legends, returning to his old stomping grounds? Or maybe Supergirl? Or what about Jesse Quick or Jay Garrick and his new protege? It could even a comic book character we haven't even met yet. I need this episode now!