John Diggle (Arrow’s David Ramsey) makes an appearance on The Flash episode airing May 15.

The episode is titled “Think Fast” Here is the synopsis from TV Guide: “When DeVoe assaults an A.R.G.U.S. facility to complete his Enlightenment Machine, Barry realizes the only way he can stop him is if he allows Cisco and Caitlin to accompany him into the facility. Still shaken by Ralph’s death, Barry isn’t sure he wants to risk any more of his friends’ lives and considers taking on DeVoe solo.”

Don’t miss The Flash “Think Fast” airing Tuesday, May15 at 8/7c on The CW.

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