The god of speed was understandably miffed that Barry confined him for what seems to be quite a long time, and he fully intends to strike back at where Barry is most vulnerable.
Unfortunately for Team Flash, Savitar moved too quickly for any of them to see, aside from Barry, Wally and a visiting Jay Garrick.
Barry apparently found a way to capture Savitar in the Philosopher’s Stone, which stops Savitar from escaping unless somebody opens it from the outside.
They jerry-rigged a doohickey to allow them to speak to Savitar through an unconscious and strapped-down Julian, and the antagonist ranted and raved about being wronged by the Flash.