Smallville (2001)

S03E18 Truth

After Chloe inadvertently breathes in a strange krypto-gas, she realizes it causes anyone nearby to reveal their deepest truths. Eager to exploit this newfound ability, she visits the Kents to uncover Clark's hidden secret. However, this power has dire repercussions, and Clark races against time to find a cure before Chloe learns his truth—or worse, faces a deadly fate.