Mindstorm adds psionic powers and renegade angels and demons to INS/MV.
Psis are humans who have developed mental powers. They're not affiliated to Good or Evil, they have their own goals and most of them are employed by corporations called "Trusts". Renegades are angels or demons who decide to quit, and either join the other side of the Great Game or just try to be left alone (which won't happen, since neither Archangels nor Demon Prince like traitors).
The book contains all the rules needed to create and play a psi character, rules for trusts and the high-tech gear they develop, a chapter describing the consequences of becoming a renegade, two scenarios ("Turlututu, chapeau pointu, tu l'as dans le c..." and "Basile, il y a un éléphant dans ma cathédrale"), and a chapter describing compatibilities between the different forces of the game (angels, demons, psis, voodoo, vikings, sorcerers...)