Jemma Simmons is S.H.I.E.L.D.'s brilliant biochemist, now the single mind holding the team's impossible journey together. She understands the refitted aircraft that carries them through time better than anyone alive, even as she admits she barely understands it at all, and it is her planning that gives them any footing in an era they never expected to reach. From the command center she coordinates the operation, and when the team captures one of the enemy Chronicom, it is Simmons who leads the interrogation, calmly escalating the intensity until its rigid programming begins to crack.. until it's too late.

Simmons turns the bar into a makeshift laboratory, bent over the green substance the wounded contact carried and refusing to take the woman at her harmless word. It is Simmons who catches the lie, a passport stamped with half a dozen recent trips to Germany and a residue on the woman's shoe that she runs down to its source: an early form of the very formula that will one day make super soldiers and bend the course of a world war.

Arriving in period dress to dig a bullet out of the wounded woman, she meets Koenig's casual contempt, dismissed as a dame and a bird, with the flat correction that she is a doctor and a biochemist. When the others argue over whether to kill Freddy or steer him from his path, it is Simmons who lays out the trap they are in: either course would alter history enough to hand the Chronicoms the future they crave, leaving the team to protect the very evil they came to undo. All the while she watches the clock, counting down the narrow window before their vessel leaves the era without them.