We can observe the invasion in the third part of the series, where in order to win (or at least try), Shepard has to gain as many allies as possible. In the second part of the cycle, Shepard enters into an alliance with Cerberus to solve the mystery of the disappearance of entire human colonies on the outskirts of the Milky Way, and hits the trail of a race of Collectors trying to speed up the approaching invasion. However, it soon turns out that the Saren is only a pawn, and the real deadly danger to the races inhabiting the Milky Way is the Harvesters, an ancient race of machines that cyclically sterilise the galaxy from organic life. As the first human Spectre, the defender of peace, the hero (or heroine, because we can choose the sex of the character being led) has to crush the plans of Saren, who not only betrayed the Council sitting in the Citadel, but also brought a threat to the whole galaxy. The main character of the series is Commander Shepard.
