The justification for Nick to become a Grimm again is made much clearer in the wake of the most recent attack against Monroe and Rosalee. At work, Nick and Hank are called to a stretch of highway that acts as a staging area for a horrifying Wesen ritual. In Vienna, Viktor meets with a completely broken Adalind, now ready to be of assistance in finding and retrieving the baby. Meanwhile, Trubel is surprised by the sudden arrival of an old friend.
Recap / Grimm S 4 E 6 Highway Of Tears
There is no mercy in you. You cut off the heads of men and women and these you wear as a garland around your neck.