From his very first public meeting in Kolkata on Friday, Mr Roy left no one in doubt of his target in the Trinamool - Mamata Banerjee's nephew and party MP Abhishek. Now, two senior bureaucrats in the West Bengal government are caught in the crossfire.
On Sunday, Mr Roy wrote to the state home secretary Atri Bhattacharya and the additional chief secretary of the MSME department Rajiva Sinha accusing the two officers of lying and aiding political activity.
The complaint was about a press meet on Saturday at the state secretariat where the two officers claimed the private company called Biswa Bangla and its logo - designed by Mamata Banerjee - belonged to the West Bengal government.
Mr Roy, however, apparently has correspondence between the state government, the registrar of trademarks and Abhishek's lawyers that indicate that the logo is Abhishek's, the state has opposed his right to it but the issue remains unresolved.
It may all seem like much ado over a logo but Mr Roy told his first public meeting as a BJP leader on Friday that Abhishek also owned the trademark of Jago Bangla, the Trinamool newspaper, and, according to some reports, also the Trinamool party's logo.
It has never been a secret that Abhishek Banerjee and Mukul Roy did not see eye to eye on several issues. In fact, even Mamata Banerjee's break with Mr Roy was over what Mr Roy may have told central agencies about Abhishek during a probe in a ponzi scheme.
What followed was the replacement of Mr Roy's men from posts in the party by Abhishek's loyalists and the side-lining of Mr Roy himself.