What attempted plot did Washington's officers devise?

I believe that you are referring to the "Newburgh Conspiracy". Congress lacked the funds to pay the officers in the army. The army (officers) were so upset they actually threatened a military coup. Washington's advisors had Washington appease them in a now famous speech. He spoke of a civilion instead of a military government. Congress was able to compromise granting five years of full pay instead of a lifetime pension of half pay.