There were three changes for the Swans with Darren Pratley, Nathan Dyer and Thomas Butler all in the starting line-up.
With six minutes on the clock Ashley Barnes should have scored for the visitors when he out-paced Ashley Williams, only to see his close-range shot rebound off Dorus de Vries who had come out quickly to block.
Plymouth's over vigorous tackling earned them two yellow cards and when Karl Duguid made it three just outside the area in the 25th minute Jordi Gomez thundered the free-kick against the visitors' crossbar.
Butler was seeing plenty of the ball down the left flank and he slipped a short pass into Scotland, but there was no power in the shot and Romain Larrieu safely gathered.
The Swans were on top, but that final ball was still eluding them as the first half drew to a close.
No changes for either side at the interval and the Swans were soon back on the attack and three minutes after the restart Scotland outwitted Argyle's central defenders, but his right-foot shot skimmed past the outside of the post.
Scotland needed attention after yet another heavy challenge, but with the Swans lacking their usual crisp and fast passing game it was another free-kick from Gomez that almost put them ahead but Larrieu leapt high to tip over.
In the 73rd minute Gomez missed a glorious chance to open the scoring when he blazed high and wide after Angel Rangel had sent him clear.
They were thrown a lifeline in the 76th minute after Larrieu could only push away a Butler shot.
As Gomez raced in to collect the loose ball the Plymouth keeper brought him down and Scotland lashed in the spot-kick for his 21st strike of the season.
The Argyle goal led a charmed life in the closing minutes, but the Swans failed to add to their score.