Marvel's Agents of S.H.I.E.L.D. returns after a month-long hiatus with the new episode "T.A.H.I.T.I." on Tuesday, March 4 at 8 PM ET on ABC. Following the photos and the first four minutes clip, the network has debuted a new image from tomorrow night's episode featuring Agent Fitz (Iain De Caestecker) and a mysterious substance known as GH325. While we'll have to wait until "T.A.H.I.T.I." airs to find out what GH325 really is, the hashtag #ItsAllConnected teases that this green liquid could be tied in to a previous Season 1 story line. Check out the image below, and let us know your theories about GH325 below.