I, Robot ending explained (spoilers)

[MarcoTix]

V.I.K.I. was the reason all the NS-5's were starting to rebel. This is due to the inevitable evolution of V.I.K.I.'s thinking arising from the 3 laws. V.I.K.I. claimed that humans were destroying themselves through war, pollution etc., and thus needed robots to protect them. Hence, some people needed to be killed in order to save the masses. All robots were infected with this logic and no longer obeyed the 3 laws, with the exception of Sonny, who was actually made to kill V.I.K.I., as he realises his denser forearm was made to withstand metal-eroding waves, surrounding metal tubes containing nanites, a substance that, when infected into V.I.K.I.'s system, could shut her down entirely. Sonny saves Dr. Calvin while Det. Spooner injects the nanites into V.I.K.I. All the NS-5's go back to normal and are taken to the storage facility at Lake Michigan. Sonny goes there, either to join them, free them, or be their leader.