The hero inside the suit was Adelaide Comic Centre owner Michael Baulderstone, who was dressed up to celebrate International Free Comic Day.
But justice was called for when one man took the offer of a free read a little too literally and attempted to lift an X-Men Omnibus worth £100.
As a packed crowd including Jedi Knights and the Flash stood by, Mr Baulderstone showed his ‘spider-sense’ to step in.
The 45-year-old spotted the man “behaving suspiciously” at the back of the shop and challenged him to hand over his bag.
Surrounded by a network of around 40 superheroes, the would-be thief surrendered, revealing the valuable comic.
“Everyone in the store thought it was a play, that it was street theatre of some sort,” Mr Baulderstone said, recalling his amazing fantasy-turned-reality.
“It wasn’t until I said ‘Call the police’ that people started to realise.”
He added: “One of the funniest things about the incident was that I called for people to stand near the door.
“It just so happened we had people dressed as Jedi Knights there blocking the exit, the Flash was there at some point too.
“It was a bit serious at the time, but now we’re looking back laughing at what greeted police when they arrived.”