"Her character is a woman who takes matters into her own hands," says executive producer Kelly Souders. "And those hands are wickedly dangerous! She won't be working with Justin but she'll have her hands full with Clark!"
Hartley will appear in Episode 8, which is titled "Abandoned."
"We are thrilled to have Lindsay on Smallville," Souders says. "We've all been looking for a fun opportunity for the last year. "
Smallville returns Friday at 8/7c on the CW.
Follow @NatalieAbrams on Twitter this week for spoilers and breaking news from the sets of Smallville, Fringe, Supernatural, V and many more.