Spencer will play Megan Hunt, the sister of Owen Hunt (Kevin McKidd). The role was recast due to original actress Bridget Regan's scheduling conflict. Regan stars in TNT's "The Last Ship" opposite "Grey's" alum Eric Dane.
At the end of Season 13, Owen learned that his presumed-dead sister was, in fact, alive. She was transported to Seattle for medical treatment. Megan's arrival should also cause a lot of angst for ex-boyfriend Nathan Riggs (Martin Henderson), who recently became romantically involved with Meredith Grey (Ellen Pompeo)
Megan's arc will likely include Kim Raver, who is set to reprise her role as Dr. Teddy Altman for multiple episodes.
Spencer will have a bit of time for this recurring gig, since production on Season 2 of "Timeless" won't begin until November. The time-traveling drama was famously canceled, then un-canceled by NBC after a passionate fan campaign.