It is the middle of the twenty-second century. Humans have been exploring the known universe for over a hundred years, and have made contact with numerous alien species; some humanoid, some not.

Earth is a leading member and staunch supporter of the Commonwealth of Planets, where along with the Parliament of Planets, is the governing body for the known universe. Earth joined the Commonwealth some thirty years before the Tyrillians, a non-humanoid species of aliens, tried to subjugate the human race by invading the galaxy.

Mark Praed is a half-human, half-alien who has lived on Earth virtually all of his life. From his Kyreen mother, he has inherited the ability to read minds. Not long out of university, he was recruited as an agent for the Commonwealth Intelligence Service. Over the last two years he used his alien abilities to run a covert operation on the alien planet of Ludmalia, but betrayal and its aftermath requires him to transfer to the Commonwealth’s counterterrorist task force.

He is paired with Alexandra Lansing, a by-the-book two year veteran. Alex is not good with change and having to take on a new partner is one change she would prefer to avoid. She has always been partnered with Henry Davison, an older operative who, after sustaining an injury, is being promoted.

Henry has romantic feelings for Alex, and he is irritated that she’s been assigned a new partner, especially one who is not human. Henry fought during the Tyrillian conflict, and so has some definite prejudices against aliens. He always protected Alex on their operations, and he finds Alex’s new partner to be too young and too independent to watch out for her. And he doesn’t trust Praed, mostly because of his alien mind-reading abilities.

This series follows Alex and Praed, and the work they do fighting terrorism throughout the Commonwealth.