Isabelle Hartley was a veteran agent of S.H.I.E.L.D. who always has a knife by her side. While dedicated to S.H.I.E.L.D., she was also had a very strong bond with her sister, Jane, who, according to Lance Hunter, was "her favorite person in the world". Her mom died about five years prior to "Heavy is the Head" of breast cancer and Hartley's sister Jane is currently suffering from the same sickness.
In "Shadows", Coulson sends Hartley and the team on a mission to steal the Diviner from a government warehouse. However, as soon as Hartley touches the artifact it causes her hand to slowly become encased in a cocoon. Idaho and Hunter rush Hartley to a hospital while the others attempt to steal a quinjet. Before they make it to the hospital, Hartley tells Hunter to cut off her arm before the Diviner kills her. However, Creel collides with their car and Hartley and Idaho both die in the crash.
In "Heavy is the Head", Hunter has Talbot erase her criminal record (since S.H.I.E.L.D. is now labeled a terrorist organization) and promise to give Hartley a proper funeral. Later, Hunter tells Coulson to send Hartley's last paycheck to her family.
- Hunter says he met Hartley through his psychotic ex-wife as she and Hartley used to be good friends.