"I resigned my contract in Greece and I wanted to come back to England. Plymouth is a good team and the manager wanted me here."
Douala was training with Charlton but with their impending relegation Charlton did not want to take him on a contract.
He has in the past been on loan at Portsmouth and has recently played for St Etienne. His biggest career move came when he signed for Sporting Lisbon in 2004.
Paul Sturrock revealed the news after today's defeat to Burnley.
He is going to need Douala to deliver immediately as Argyle face a battle to stay in the Championship.