Does Defectors do anything when triggered by Five-Year Plan
If Defectors is triggered by Five-Year Plan during the Headline Phase, it cancels the USSR event if it hasn't happened yet. From the Twilight Struggle FAQ:


  Q: If Defectors is not selected by the US, but a Headline
  event causes it to be played, is the USSR Headline event canceled?
  
  A: If the event that caused Defectors to be played would be executed before
  the USSR event, then that event is canceled. If the USSR event has already
  been executed, it is not canceled.


However, if Defectors is triggered as an event during the US Action phase, the event occurs, but no VP is gained (because it's not the USSR Action Round).