Barry and Savitar finally come face to face on The Flash in "Cause and Effect," and it is an enlightening confrontation to say the least. After realizing that Savitar was his future self in last week's episode, Barry forces Savitar to reveal what he really is — a time remnant. Now that Team Flash knows what Savitar is, they might just have a chance. So, how can Barry defeat Savitar on The Flash? Well, before they can come up with a strategy, they first have to figure out a way of stopping Savitar from knowing what they're doing. Unfortunately, their solution is to accidentally give Barry amnesia, thus erasing all of his memories. Long story short: it isn't very successful.
Luckily, while Barry is waling around without his memories, Team Flash newbie Tracy Brand is hard at work on creating her Savitar prison. And, by the end of the episode she's crafted the speed bazooka, a gun that could theoretically trap Savitar in the Speed Force. However, for the speed bazooka to work, it needs a huge amount of energy, the likes of which is almost unheard of on this Earth. Which leads us to...King Shark. Remember the giant shark who became man-like and started killing people in Central City in Season 2? The episode ended with a shot of King Shark swimming around in a sort of tank with a glowing red orb — the energy source.
Now, the last time we saw Killer Shark, he was taken into ARGUS custody by Lyla, aka Diggle's wife on Arrow. Assuming he's still there, that means that the red orb of energy Team Flash needs to defeat Savitar is also the property of ARGUS. Something tells me they're not just going to hand it over.