Plot summary
Since being resurrected by S.H.I.E.L.D.'s Project T.A.H.I.T.I. using the experimental drug GH-325 (derived from the alien corpse Carter discovered in Whitehall's possession), Coulson has been compulsively carving alien symbols. When a former S.H.I.E.L.D. agent and patient of T.A.H.I.T.I. is killed and her body carved with the symbols (by the former agent who had carved the painting previously), Coulson uses Hydra's memory machine to find other patients who were injected with the drug.
He goes after the remaining patients, trying to find an end to the madness. He discovers that the writing is actually a 3D diagram of a city where the alien host of GH-325 apparently wished to go. Seeing the completed design ends his need to carve but, since Hydra is also searching for the city, he makes it a priority for S.H.I.E.L.D. to find it first. Meanwhile, the other members of the team try to capture Ward, who betrays Hydra by capturing Bakshi and leaving him for S.H.I.E.L.D. before preparing to meet his brother.
Credits
Adapted from Wikipedia contributors, Agents of S.H.I.E.L.D. season 2. HTML formatting and reference markers removed.