Superboy first confronts the masked criminal who calls himself the Mechano-Master when the villain appears in the Boy of Steel's hometown of Smallville. The villain possesses powerful weapons that are capable of harming even the Boy of Steel. Using these weapons against the hero, the Mechano-Master forces Superboy to be humiliated for fear that the crook will set off explosions in Smallville.
Superboy is finally able to corner the Mechano-Master inside his flying fortress, and, unmasking his opponent, discovers that the villain is in fact an adult Lex Luthor. Luthor explains that he used a time ray to send Superman's Fortress of Solitude back in time to when the sun was red. However, a malfunction caused Luthor and the Fortress to instead be sent to Superboy's time, where Luthor uses the various exotic weapons contained within the Fortress to battle Superboy as the Mechano-Master.
Repairing the Fortress, Superboy sends it and Luthor back to their proper time in the near future. However, both Superboy and Lex are exposed to Amnesium gas, which causes them to completely forget the entire encounter (SB No. 135/1, Jan 1967: "The Menace of the Mechano-Master").
The identity of the Mechano-Master that Lex Luthor employs in this tale should not be confused with that of the Mechanical Master, an unrelated villain that Superboy encounters in a 1979 chronicle (SF No. 193/1, Feb 1979: "The Menace of the Mechanical Master!").