I think the "plot" sense is much stronger here. The "deceive" meaning is merely inherent, because in order to successfully plot the plot must not be discovered, hence the element of deceiving.
People can plot, but if the plot is detected or averted, then no deception has taken place. But if a person is deceived....he is deceived.
So the first sentence includes an assumption of deception, while the second includes an assumption of skullduggery. I believe the latter also carries more of a connotation of insidiousness or conspiracy.