A list will appear showing all the people 15 levels below and those above you who are doing convoy in your server. You get 3 plunder attempts daily as compared to 4 convoy attempts. If you fail the plunder, you will get 0 rewards. Every plunder action will consume 1 plunder attempt regardless of the result. Also, if you fail the first plunder attempt you can try plundering again the same person if you're being obnoxious. ;P