Farthest Star

Cuckoo was coming. No one knew what is was - but everyone knew it was trouble. Designated Object Lambda when it first appeared on the fringes of the galaxy, 20,000 light-years away, it was traveling at one-sixth the speed of light. The astrophysicists said thet it was vast... light... and had the potential for utter destruction. So an exiting space probe was reoriented to intercept; it was staffed with replicates of both humans and aliens. Then the space probe began to leak radiation...