In the spirit of the pantomime season, here's a warning for the most senior members of Sinn Féin: "Look out, he's behind you".
Or alongside you. Or worse, leading you. And in glorious pantomime tradition, you are oblivious to his presence!
So-called "dissident republicans" believe they always saw traitors in their midst. They may feel now even more reason to suspect that the entire political strategy of the Sinn Féin leadership in recent decades – which, to their minds, has compromised and abandoned the republican vision of an united Ireland – has been manipulated by the Brits.
That might be stretching things, but the ability to broker a good deal may have been compromised by the British having information from the likes of Denis Donaldson.
And if a prison friend of Bobby Sands has taken the Queen's shilling then the suspicion must be that the speculation of recent days – that others more senior within the IRA/Sinn Féin have been recruited too – is correct also.
But it's not just Sinn Féin who should be worried. If perfidious Albion has planted spies successfully at the heart of Sinn Féin the question has to be asked where else do they reside?
Within the SDLP? Within the political parties south of the border, either at elected level or within the ranks of advisers and strategists? Within Government? Within RTÉ? Within the national newspapers? Within the Garda, as former Research Force Unit spy handler Martin Ingram alleged on Monday? Paranoia may be rampant in many institutions this week.
And then there are those who effectively have been doing the British work in undermining republicanism without even having to be paid for it. There are always those who would do the bidding of the British without requiring financial reward, because they believe they have common cause in defeating the IRA. They would regard themselves as patriots, others might see them as useful idiots.
Sinn Féin, of course, is appalled by the "bad faith" shown by the Brits, as if spying is somehow worse than the IRA's decades of murders and as if republicans would never engage in a bit of subterfuge.
But does anyone believe that the IRA and/or Sinn Féin haven't engaged in their own bouts of espionage over the years?
Isn't it credible that what the Brits have done to Sinn Féin is exactly what that party has being doing itself throughout Ireland? Isn't that what led to the conviction of Aengus O'Snodaigh's good friend Niall Binead?
Isn't it possible that Sinn Féin has planted its own sleepers and spies within the heart of the domestic political and media establishments too as part of its own plan to seize power? They may not be party members but is their any doubt that their ideological bent is unhesitatingly republican and that their work is informed by that?
It may be the type of argument Michael McDowell likes to push but that doesn't mean it's implausible.