What is more worrying is a run of results at Vicarage Road that now reads one point taken from the last 15 available.
That is relegation not promotion form and it is rendered even more bizarre because Watford have one of the very best away records in the country.
But it is home results, more often than not, that secure elevation and the Hornets need to get back on track and quickly.
Although it was another below-par showing by Boothroyd's men, it looked like they would at least have the consolation of back-to-back clean sheets until a minute from the end of normal time.
Then Barry Hayles went rampaging away down the right and although the impressive Peter Halmosi failed to connect with his cross at the near post, the unmarked David Norris was in the right place to tuck home the winner.
It was no more than Argyle deserved. Both Norris - stabbing wide with the goal at his mercy - and Nadjim Abdou, who missed the target with a gilt-edged header, should both have scored after a dull opening period, while the best the shot-shy home side could muster was a Tommy Smith shot that hit the woodwork.
In many respects though, the game was a sideshow to the main event at half-time. That was when an emotional Al Bangura was joined on the pitch by Hornets chairman Graham Simpson and local MP Claire Ward to continue publicising the plight of the young midfielder, who is on the verge of being deported back to his native Sierra Leone after losing an immigration hearing earlier this week.
The Hornets have since embarked on a mass media offensive and the 19-year-old, who has also become a father recently, was moved to tears as he was applauded by all four sides of Vicarage Road.
The fact his team that went on to lose did not seem so important in the overall scheme of things.