I expected something clever like that being a dummy napkin for him to burn and be confident he's clear or some other clever method, not here Helen remember you can make the house explode and survive unscathed to then press a button that makes the Mona Lisa burn before the killer with a gun stops you...

Yeah but that wasn't the original plan, Helen found the key evidence and for some reason took the original in front of the killer who, by this point, still should have a gun... And when he burns it she and Blanc figure the destruction plan out, which depended on her being able to reach that button before the guy with a pistol on hand. Pretty dumb ending.

Similar opinion here, I liked the setting and the development but once we got to the big 3rd act reveals things got really dumb real fast and not just from the bad guy but from the good person, it seemed nonsensical how they arrived to the destruction instead of something like recording the bad person confessing or something like that...