Enemy of My Enemy
"Enemy of My Enemy" is the ninth episode of the fourth season of the Fox science-fiction drama television series Fringe, and the series' 74th episode overall.
The episode was co-written by Monica Owusu-Breen and Alison Schapker, while being directed by Joe Chappelle.
Plot
Following from "Back to Where You've Never Been", the alternate universe's Olivia and Lincoln track down David Robert Jones to a warehouse, unaware that Colonel Broyles had alerted Jones to their arrival. Jones waits until Olivia and Lincoln arrive before destroying one of his beloved shapeshifters, warning that if he's willing to destroy someone he loves, they should fear what he would do to anyone else. He asks to be taken to Fringe headquarters.There, Peter and the prime universe's Lincoln, having been cleared to return to the prime universe, are present when Jones is escorted to an interrogation room. Peter recognizes Jones, whom Peter has killed in his original timeline, and offers to interrogate him; Peter is able to throw Jones off guard, revealing that he knows Jones had crossed over from the prime universe and that his scars showed he'd suffered injuries as a result of being teleported out of prison. Jones makes a demand for a hard drive, containing satellite tracking data, to be returned to him and to let him go or else his agents will launch terrorist attacks; this is demonstrated when one agent sets off a biochemical agent in a hospital ward, killing all inside.
They let Jones go after secretly fitting him with a tracking device. However, due to Broyles' interference, Jones is able to elude the tracking system, leaving the prime version of Lincoln suspicious of a mole within Fringe division. Peter and Astrid study the data from the hard drive, and identify that Jones appears to be looking in a nearby quarry for amphilicite, a mineral in appreciable quantities that when processed correctly can create a hole in the universes. Peter realizes too late that the maps are those of the prime universe; Jones has crossed back over with help of his shapeshifter agents there to access the quarry. Peter and Lincoln return to the prime universe to catch up to Jones, but arrive too late as Jones takes a load of the mineral back to the alternate universe. The two Fringe teams meet and agree they must work together to defeat Jones, even though they know that Jones has been ahead of them. Peter recognizes that he knows Jones from the alternate timeline and is a variable that Jones has not accounted for. Later, the viewer is shown that Jones is communicating with Nina Sharp, who is preparing an unnamed woman for "Phase Two" of their plan.
Meanwhile, Walternate and his wife Elizabeth discuss helping Peter. Elizabeth crosses to the prime universe to meet with Walter and to gain his help to assist Peter, which he has been reluctant to do, believing he has been given no sign of absolution for taking Peter from her. Elizabeth assures him that she had forgiven him long ago. Walter returns to Peter that evening and offers Peter his help to return home.