As season four begins to wind down, there are major changes underfoot at All Saints. “Chaud & Froid,” the French term for hot and cold, not only deals with the water Jackie (Edie Falco) and Dr. Cruz (Bobby Cannavale) use to revive Charlie (Jake Cannavale) from his drug overdose, but with some vacillating feelings between Jackie and Zoey (Merritt Wever), and Dr. O’Hara (Eve Best) and Coop (Peter Facinelli). This very interesting installment perfectly sets up what’s to come in the remaining two episodes of this amazing season.