On July 28, 1835, he took his 20-barreled Death-o-Matic and aimed it down at the boulevard du Temple, where King Louis was about to cross the street accompanied by his sons and staff. As soon as they were in his various lines of fire, Fieschi set the machine off, exploding bullets all over the place. He somehow missed his intended target--Louis and his children were only grazed by the hail of bullets--but he did manage to hit a very large number of people, including himself (why he taped that one gun on backward, we'll never understand).
Fieschi ended up with severe injuries from the explosion, which prevented him from fleeing the scene while twirling his mustache and muttering "Blast!" But Louis, to Fieschi's surprise, made sure no expense was spared in saving the man's life. Fieschi decided to take advantage of this opportunity to finger every last one of his accomplices, confident that he would be pardoned, since the king had done so much to save him already. He ended up being even more surprised when he was sentenced to death by guillotine, for attempting to murder the king with something a 12-year-old would draw in his Five Star.
"Dammit, Louis, I thought you were cooool!"