When it first began, Agents of S.H.I.E.L.D. acted as an offshoot of Marvel's larger cinematic universe, using Agent Phil Coulson (Clark Gregg) as a bridge and expanding upon the secret agency that had appeared in the movies. Toward the end of season 1, AoS drastically changed as a result of Captain America: The Winter Soldier - which revealed the infiltration of Hydra and subsequent unraveling of S.H.I.E.L.D. However, in season 2, AoS began to build and explore the mythos of The Inhumans, prior to the film's release in 2019.
One character introduced along with the other Inhumans at their settlement, Afterlife, was Lincoln Campbell, played by Luke Mitchell (The Tomorrow People). Although the season 2 finale of AoS saw a massive shake up in the structure of the Inhumans' society, Lincoln will be back for the third season.
Marvel has announced that Mitchell has been promoted to a series regular for the upcoming season 3. The actor debuted in episode 16 of season 2 as Lincoln, an Inhuman with the ability to manipulate electricity. He became a mentor and friend to Skye (Chloe Bennet) and, when the leader of Afterlife Jiaying (Dichen Lachman) started a war against S.H.I.E.L.D., Lincoln sided with Skye and her teammates.
Jeph Loeb, executive producer and head of Marvel TV, spoke about Mitchell joining the cast and Lincoln's role in season 2:
“Luke proved a valuable addition to our cast in Season 2, and after seeing him light up the screen with his charisma we knew we had to have him back for more. Our writers have come up with big plans for the character of Lincoln in our next season, and we can’t wait for fans to see everything we have in store.”
In the season 2 finale of AoS, the series left many story threads hanging that will be explored throughout season 3. In one, it was revealed that particles from Jiaying's Terrigen crystals made their way into Omega-3 pills on shelves, which will lead to more people undergoing Terrigenesis - the transformation that grants the Inhumans their powers. Additionally, Coulson spoke of Skye heading up her own team of powered people under the umbrella of S.H.I.E.L.D.
When viewers met Lincoln in season 2, he worked as a transitioner, helping those that arrived at Afterlife to understand the history and customs of the Inhumans. As such, he may fill a similar role in season 3, both in teaching S.H.I.E.L.D. about the Inhumans - perhaps offering insight into the Kree weapon they’re holding - and those who undergo Terrigenesis.
Or, it's possible that Lincoln could become a part of Skye's team, and perhaps a S.H.I.E.L.D. agent. After aiding S.H.I.E.L.D. in the war with Jiaying and demonstrating his fighting abilities (with his Inhuman powers), he could prove a force to be reckoned with.
Whether or not he becomes more involved with the Inhumans or joins Skye’s team remains to be seen. Of course, we won’t know more about Lincoln’s role next year until we learn more about how the show will proceed in the upcoming third season of Agents of S.H.I.E.L.D.
Agents of S.H.I.E.L.D. returns for season 3 fall 2015.