The police catches Phantom Thief 001, an amazingly gifted but also
pretty cowardly cat burglar, red-handed - but only minutes after the
arrest, the Phantom Thief is freed by the Iron Cross Army led by super
villain Professor Monster (Mitsuo Ando). Actually the Iron Cross Army want
to use the Phantom Thief as a fake Spider-Man to discredit the real
Spider-Man - bike racer Takuya (Shinji Toudou) in real life - and lure him
out into the open.
And even though Spider-Man knows he's walking into a trap, he walks
into the trap and soon enough he dukes it out with several of the Iron
Cross Army henchmen before he faces another Machine Bem - a monster that
can grow to any size - and has to call in his giant robot
Marveller/Leopardon to fight and defeat the giant monster.
Silly fun, there's not much more to say about this. If you're in a
philosophical mood, don't watch, but if you like cheap and cheesy giant
robots and monsters, this might be your thing.