Smallville: Season 7, Episode 6

7 - 6: Lara

Clark learns Kara is in Washington searching for the crystal. Kara is captured after she breaks into the lab and sedated with a kryptonite-infused truth serum. The serum causes her to relive a prior trip to Earth when she followed Clark's biological mother, Lara, to the Kent farm. Clark arrives in time to save her but, after searing the machine with heat vision, he also falls victim to the serum and sees what Kara sees: his mother.