Babylon 5: The Legend of the Rangers: To Live and Die in Starlight

The Rangers, an order of warrior-priests, have wandered the darkness between the stars for over a thousand years, protecting a hundred worlds from invasion and destruction. But now a new alien threat appears on the even horizon of the Intersteller Alliance, a force more ancient and powerful than anything previously encountered. The only obstacle in the way of this new race: a single, broken-down Ranger ship, under the command of David Martel, whose sole orders were to escort Ambassador G'Kar to an interstellar conference. Alone, barely armed, they must defeat an enemy unlike anything they have seen before...