It looks like the cable housing is half out of the "ferrule".

TO REPAIR:

1) shift to smallest cog (release as much cable as possible.

2) remove rear wheel

3) pull housing back, and then insert into "ferule", making sure the entire housing slips into the holder.

4) install rear wheel.

5) ride.

In theory, there should be enough cable slack / derailleur movement possible when you are in the smallest cog to make this possible. DO NOT LOOSEN THE SET SCREW, or you will lose the real cable adjustment. Then you're probably paying the LBS to adjust your shifting.

Or if your shifting is less than perfect now, take it to LBS, and for the less than $20 you should be not only fixed, but also properly adjusted.