The former treasurer was full of arch, Cheshire Cat-like non sequiturs and half-cloaked accusations that faded immediately to leave only the unmistakable outline of the famous Costello smirk. "If I'd wanted to be a threat to Malcolm Turnbull's leadership, I could have put up my hand on any one of, you know, 100 days and nominated for the leadership," he said at one point, amid ceaseless book plugs (the phrase "as I write in the book", or variations thereof, was used eight times). "The fact that I didn't meant that he was entirely secure. If I'd wanted to, I could have." This is a brilliant, Wonderland-style explanation of the situation that existed within the Liberal Party from the very moment Turnbull took over as Liberal leader. Costello could have crushed Turnbull at any time, but chose not to; in Costello's eyes, this earns him further credit within the party, to add to the brownie points he generously awards himself for more than a decade of not challenging John Howard.

This year must have been quite a satisfying period for Costello, allowing him as it did to return to the field of cat-and-mouse leadership strategy, this time - for the first time in 12 years - playing the role of the cat. But you could equally understand why Turnbull didn't share his enthusiasm. For Turnbull, one of the most psychologically crippling aspects of Costello's political dance of the seven thousand veils this year has been that he simply cannot understand an adversary who behaves like that. One who fades in and out of the picture, delivering a wink here, and a quizzical grin there, unwilling to throw a punch but never quite returning to the dressing rooms. There is nothing in Turnbull's past to suggest that he has any idea how to tackle the passive-aggressive approach that is Costello's hallmark.

Turnbull is aggressive-aggressive, and that's that, and the nebulous threat of Costello drove him to distraction, because it disabled all three of Turnbull's customary responses to threat: Crush It, Buy It or Sue It. I mention all this mainly because it's useful in understanding what was going on that week when Parliament turned into Wonderland. We all started in on this weird and wondrous chase after the elusive, lippety-loppity form of Godwin Grech, who now is blessedly - if temporarily - safe in the arms of Canberra's mental health professionals. Incidentally, it is now reported that Senator Steve Fielding is trying to get in touch with Grech, to seek his counsel over the structure of a possible Senate privileges inquiry into the whole affair. Poor Grech. He already has some pretty serious problems - from depression and job security issues to the regular small bowel obstructions which were rather too plentifully mentioned in this week's audit report to make that document anything like advisable breakfast reading.

To a man such as Grech already so benighted by circumstance, overtures of friendship from Fielding might seem like the latest of fate's cruel blows. Still, he started it, I guess. Back to Turnbull, and the mind games of the Cheshire Cat. It's entirely relevant that the Grech affair came to a head in the same week that Costello finally climbed out of the ring and headed for the showers. The effect on Turnbull was immediate, and visible. He was like a man who had had a large Bulldog clip removed from his brain. He could not keep from smiling, even in Parliament as he delivered the obligatory lament about the loss of such a talented Coalition asset. Imagine how bulletproof Turnbull must have felt. His enemies, falling before him unsmitten! The promise of a prime ministerial scalp hovering - unseen by all except Turnbull himself - just around the next bend! All of a sudden, he was once more the Turnbull of old, before whom in happier times Fate itself seemed to doff its cap. Costello made his announcement on the Monday of that week.

It's no wonder that, in such a mood, Turnbull took it upon himself on that Wednesday night to deliver a fatherly word of advice to the Rudd staffer Andrew Charlton, in whose precocious intelligence Turnbull would doubtless recognise an echo of himself at 30. And no wonder at all that Turnbull, having thus thoroughly tipped off the PM's office, would then overplay in lordly fashion his accusations against Rudd and Swan on the Friday. One cannot blame the Cheshire Cat directly for all this, of course. One simply notes the imprimatur of his grin. Costello was quick to point out this week that he would have been more cautious than Turnbull in transacting the OzCar affair, and that he would never have allowed the film crew from Australian Story into his office, as Turnbull did, to capture the inner workings of the debacle for posterity. He is free to make these remarks. The net effect of his own decisions is that he will never have to prove empirically that he would be less hopeless as Liberal leader than any of the poor boobs who have actually had a shot at it. Just what would it take, at this stage, for Costello to quell the talk among Coalition fantasists about his triumphal return? That's a very tough question.

Even if Costello arranged to be run over by a bus on Commonwealth Avenue, than have his body burnt on a funeral pyre of old budget papers out the front of Parliament House, there's nothing surer than that within days senior party sources would be quoted around the place with cautious messages of hope. Loading "Sure, on the face of it you have to take him at his word," you can almost hear them saying. "But as anyone who saw the 1990 Jerry Zucker film Ghost knows, there is absolutely nothing that would prevent Peter Costello's spirit from returning to Earth and leading the Liberal Party with the help of a wisecracking psychic played by Whoopi Goldberg." I wouldn't rule out the whole staged-death thing, by the way - there's bound to be a further update to the memoirs at some point and Costello will need another gimmick for that, so save your old budgets, folks, just in case.