S1·E12 When the Rat's Away the Mice Will Play

Batman manages to escape the Riddler's death trap. He and Robin decide to lay low until they can figure out the Riddler's caper. Meanwhile, the Riddler frees King Boris, who brings a gift to a major monument in Gotham City. It turns out the Riddler has substituted a bomb for King Boris's gift and he is demanding a ransom. The Riddler, though, overplays his hand, enabling Batman and Robin to capture the Riddler and his gang.