He's an unlikely looking assassin. Lithe and lean he isn't.
And while he bared his teeth for only about five of his allotted seven minutes during the emegency debate on hacking, the bite of the man MPs call "Tommy Two Dinners" certainly left its mark.Tom Watson's physique is more like that of a barrel-shaped, immovable nightclub bouncer.
An enforcer, certainly. He did that for Gordon Brown often enough.
But on phone hacking, the enforcer has become Labour's attack dog.
While Chris Bryant, who opened the debate, was all moral high ground, talking about "decency", "humanity", "morality" and so on, Tom Watson went for the jugular.
All menacing stuff!James Murdoch should be suspended, he said, for authorising a cover-up of criminal behaviour.
"This is nothing short of an attempt to pervert the course of justice," said Watson.
He claimed Rebekah Brooks "was not only responsible for what was going on, but knew what was going on". Her story was "not believable", he said.
And ominiously for Andy Coulson, he said the Tommy Sheridan trial - where Coulson gave evidence and denied knowledge of hacking - was "unsound and may need revisiting".
Dominic Grieve, usually such a safe pair of hands, was torn apart by interventions from all sides of the chamber, not on hacking but on the BSkyB/NewsCorp takeover, which was clearly not in the Attorney General's brief.But if Murdoch, Brooks and Coulson were the chief targets of Labour's onslaught, there were some big losers on the Government benches too: David Cameron, Jeremy Hunt and Dominic Grieve.
Despite Cameron conceding a hacking inquiry straightaway, Ed Miliband had his best PMQs since becoming Labour leader. He was well-argued, calm and reasonable and had Cameron on the defensive and rattled.
"I know this is difficult for him," Miliband taunted the Prime Minister. A reference, no doubt, to that cosy Christmas dinner party in the Cotswolds chez Brooks attended by David and Samantha Cameron.
One into the allegations that the police were feeble, negligent, colluding with the News of the World or taking backhanders.He was muddled and confused about whether it was for the Government or the media regulator Ofcom to refer the bid to the Competition Commission following the latest revelations.
And while normally reliable Grieve was floundering, tall, skinny Jeremy Hunt sat next to him like a stuffed tailor's dummy, mumbling and waffling, but never once rising to his feet to rescue his learned friend.
So at the end of the three-hour debate and PMQs beforehand, what had we learned?
Apart from more allegations, conspiracy theories and ritual Murdoch-bashing, that is
We learned from Dominic Grieve - or so I thought - that when David Cameron talked in PMQs about "inquiries" there are likely to be two:
Tory grandee Nicholas Soames was the first to demand it and there were many similar calls throughout the debate.And another into the hacking allegations against the News of the World and - as many MPs pointed out during the debate - other newspapers as well.
We also learned that there is now a consenus demanding a "pause" in the BSkyB/Corp takeover process.
And towards the end of the debate, a lone voice, Tory MP Therese Coffey, spoke out in defence of News International and said: "There is a witch-hunt developing against Rebekah Brooks".There were other entertaining highlights too:
The Press Complaints Commission was compared it to a "chocolate teapot" and a "fishnet condom" by LibDem MP, Adrian Sanders as he accused the press watchdog of being "toothless".
Early on, Labour's old warhorse Frank Dobson had MPs laughing when he declared: "Were News International, with their record of wrongdoing they have admitted so far, to apply to run a minicab firm in London, they would not receive a licence."
But by then Labour's menacing assassin, Tom Watson, had left his mark.