artifice \AHR-tuh-fus\ noun
Meaning
1 a : clever or artful skill : ingenuity b : an ingenious device or expedient
*2 a : an artful stratagem : trick b : false or insincere behavior

The clip fell, brushing the side of the table, and lodging itself firmly in the pile of the carpet. No one would see it again for forty years. The artifice of the clever slip was that now it would be impossible for anyone to understand what had happened here, so important was the evidence to the crime. Whether she had done it by accident, or an unconscious decision, was not clear. But it would keep her out of jail.