Complex sentence: As part of their grand scheme, they sent out cube-shaped probes that could effect a mind-swap with any intelligent creature who found one, whereby Yekubian agents could infiltrate the finder's world.
Split into simpler sentences: As part of their grand scheme, they sent out cube-shaped probes that could effect a mind-swap with any intelligent creature who found one. In this way, Yekubian agents could infiltrate the finder's world.