Did Mirakuru Return to 'Arrow' in "Next of Kin"?

Arrow began a sort of new normal in tonight's episode, but it might have ended with a familiar threat.

Spoilers for tonight's episode of Arrow, 'Next Of Kin', below.

The episode saw John Diggle (David Ramsey) adjusting to life as the Green Arrow, after Oliver Queen (Stephen Amell) passed the mantle off to him. But with Diggle still feeling the after-effects of the explosion on Lian Yu - particularly, his degenerative nerve damage - he worried about his abilities in the field. At the end of the episode, Diggle was shown meeting someone in a dark alleyway. He received a vial from them, which he proceeded to inject into his arm.

While the substance in the vial could be a number of things, we couldn't help but wonder... is it Mirakuru?

As Arrow fans will remember, Mirakuru is a super-soldier serum that ended up on Lian Yu. Oliver injected Slade Wilson/Deathstroke (Manu Bennett) with the serum, and Slade later used his blood to reproduce the serum. The drug swept through Star City, creating an army of super-soldiers.

Ultimately, S.T.A.R. Labs came up with a cure for Mirakuru - but it was never explicitly said what happened to the remaining formula. It very well could be that Mirakuru lived on, and Diggle is injecting himself with a newer formula of it.

If it does end up being Mirakuru, it could lead to a pretty interesting conundrum for those involved with the show. Dig having a new string of Mirakuru in his system - one with possibly different side effects - would definitely complicate his tenure as the Green Arrow. And it also would create an interesting dichotomy when Slade returns, seeing as he now has Mirakuru out of his system.

Fans will just have to keep watching Arrow on Thursdays at 9/8c on The CW to find out.