What happens when playing a single Treasure Map?
No,

The single Treasure map will get trashed first before you can Scheme it.  From the Seaside rules:


  Treasure Map - You can play this without another Treasure Map
  in your hand; if you do, you trash this and gain nothing.


Scheme reads:


  At the start of Clean-up this turn, you may choose an Action card you have in play. If you discard it from play this turn, put it on your deck.


If the Treasure Map stays in your hand, it is not a valid target for Scheme.  If you play the single Treasure Map, it will trash itself before Scheme triggers at the start of Clean-up.