In the darkest days of WWII, five superheroes—Captain America, Bucky, the Sub-Mariner, the Human Torch, and Toro—came together to battle the Hordes of Hitler!
Giant-Size Invaders 1 recounts the origin of Captain America in a flashback scene as young scrawny Steve Rogers drinks Dr. Erskine’s Super Soldier Formula. Almost immediately after Rogers drinks the formula, Dr. Erskine is shot and killed by Nazi agent Kruger who had infiltrated the secret lab where the Super Soldier Formula had been developed.
The origin of Master Man is also recounted. Dr. Erskine’s assistant, Dr. Anderson, is kidnapped by Colonel Kreighund and forced to reveal what information he knows about the original Super Soldier Formula. A variation of the original formula is given to a young gaunt German youth who is transformed into the Master Man. The formula, however, proves to be unstable.
The Human Torch and Toro, who had been assigned to secretly guard Dr. Anderson, descend on Colonel Kreighund’s location to attempt a rescue. During the battle between the Torches and Master Man, Colonel Kreighund shoots Anderson and escapes. The Torches fly Anderson to the hospital where they meet up with Captain America and Bucky. At the hospital, Anderson remembers overhearing Kreighund’s plans, and the group of heroes rushes to disrupt the Nazi’s plans.
In the Atlantic Ocean, Master Man begins an assault on a navy battleship only to discover that Prince Namor the Sub-Mariner is aboard. A battle ensues. As Master Man seems to be gaining the advantage over Namor, the other four heroes enter the fight. Shortly into this renewed battle, the unstable formula Master Man had taken breaks down, and he reverts to his pre-Super Soldier Formula state and is captured.