Don't worry, Simmons. Agents of SHIELD's Fitz will find you come hell, high water, or mysterious Kree stone.

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Jemma Simmons (Elizabeth Henstridge) disappeared into an enigmatic alien stone last spring, and now that the Agents of SHIELD season 3 premiere is just around the corner, Fitz (Iain De Caestecker) is prepared to redouble his efforts to find the missing scientist. After months of searching, the engineer will be ready to take drastic measures.

"On the season premiere episode, 'Laws of Nature,' when Coulson and the team discover a new Inhuman, S.H.I.E.L.D. comes face to face with another organization searching for powered people," ABC announced on Monday. "And still reeling from Simmons' dramatic disappearance, Fitz goes to extreme lengths to try to learn how to get her back."

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Unfortunately for Fitz, his mission will be a solo one. Busy with an outbreak of Inhumans, the rest of Coulson's (Clark Gregg) crew will have already written Simmons off as a lost cause.

"What happened was so crazy and there was no trace of her, that what do you do?" Henstridge explained to Zap2It. "I think that the whole team has tried and nothing has worked, so at some point you have to go, 'She's gone, we have to move on.' But Fitz refuses to do that."

Find out what repercussions Fitz's endeavor will cause when Agents of SHIELD returns to ABC on Sept. 29 at 9 p.m. ET. Check out a new promo below.