The Devils went down by 22-points (56-34) in the deciding leg, which meant they lost by 20-points (100-80) on aggregate.
Kenneth Hansen, guesting for the unavailable Ryan Fisher, was feeling unwell and failed to score. That was after the rider replacement facility for Fisher produced only three points in the home leg on Friday evening.
Co-promoter Ashley Taylor said: “The absence of Fisher was a big blow. It meant we effectively scored only three points from our number one over the two meetings.”
So Glasgow will go on to meet Somerset in the play-off semi-final while Plymouth will call a halt on the 2015 season.
There had been plans to stage an individual meeting on Friday to round-off the season. But those plans have been dropped because Todd Kurtz (injured), Ryan Fisher, Jack Holder and, possibly, Linus Eklof would be unavailable.
Co-promoter Ashley Taylor said: “It would not make any sense to try to go ahead with an individual meeting if only three of our regular team members are available.”
Plymouth will hold their end of season presentation evening in the Mount Edgcumbe Masonic Hall, Citadel Road, Plymouth, on Saturday evening (October 10) with tickets priced at £10 each.
GLASGOW 56: Aaron Summers 15, Richard Lawson 13+2, Nick Morris 11, Victor Palovaara 6+2, Hynek Stichauer 4+1, James Sarjeant 4, Kauko Nieminen 3+2.
PLYMOUTH 34: Linus Eklof 11+1, Morten Risager 9+1, Kyle Newman 8, Jack Holder 3+1, Sam Simota 3, Kenneth Hansen 0, Todd Kurtz r/r.