Alex Salmond was missing from First Minister's Questions today - he's off to inform America about the benefits of independence this week.

So it was down to his deputy, Nicola Sturgeon, to engage Johann Lamont in a spot of trench warfare before lunch. They did not disappoint.

After the Unionist camp's weekend currency cropper, the Labour leader avoided any talk of the pound by speaking exclusively in dollars.

In particular, the 2000 bucks it costs for a night at the Chicago Peninsula Hotel, where the FM bunked during a Ryder Cup beano in 2012, and about which the government still refuses to answer freedom of information (FoI) requests.

It was an obscure topic, but there was a logic to Labour's nitpicking - it drew Ms Sturgeon into the long-running 'mystery bill' saga.

If, as Labour feverishly pray, the FM blew a bundle of taxpayer dough living it up in the windy city, and his deputy defended him, then she too would be tainted if a grubby bill emerged from the government files.

Ms Lamont said that when she last raised the Chicago stay at FMQs in January, Mr Salmond said an FoI request would be answered "as so soon as possible...why should it not be?"

However, the government later refused to release details of the stay on security grounds. What was all that about then? asked Ms Lamont.

The DFM declared herself "flabbergasted" at the question, and said all the info about the trip was already in the public domain.

Ms Sturgeon reminded the chamber the FM was in the US for Scotland Week, a cut-price version of the old Tartan Week plugged by infamous blouse-wearing Labour FM Jack McConnell.

Under Jack, the Scottish government spent £1m on Tartan Week - three times the current bill. The SNP clearly got better value for money.

But Ms Lamont wouldn't budge, demanding to know "how much taxpayers' cash Alex Salmond spent on himself in the Peninsula Hotel?"

Not that our politicians are petty, you understand, but Ms Sturgeon retorted that Jack McConnell used to stay in New York's Benjamin Hotel, as "frequented by Paul McCartney".

Oh, and Ms Lamont was only banging on about hotel bills because she had "no positive programme of her own".

But what about transparency, asked Ms Lamont? "The Scottish Government doesn't want to explain how much taxpayers' cash Alex Salmond spent on himself. No accounting is given."

Right. Ms Sturgeon had had enough. She sighed, cracked her knuckles, and let rip.

"This is desperate stuff from the leader of the opposition. What Johann Lamont has chosen to do today, not for the first time and I'm pretty sure not for the last time, is indulge in smear and insinuation instead of discussing the real issues of the day.

"It's probably one of the reasons Labour is in the sorry state it's in in Scotland today."

Never one to duck a demeaning rammy, Ms Lamont said the FM was "unadjacent to the truth".

No gouging or hair-pulling, shouted deputy presiding officer Elaine Smith, although it came out as an exasperated "Order! Order!"

But to no avail. The DFM fixed bayonets. "Johann Lamont can smear the First Minister as much as she likes," she snarled.

This generated a kaleidoscope of ghastly mental images - smear the FM with what? Mud, suntan lotion, custard? Our lustrous North Sea oil? (It would probably take a barrel or two.)

Even the hardiest MSPs looked pale and woozy. "And she can smear me as much as she likes," Ms Sturgeon carried on. MSPs started to faint.

"But the real question Johann Lamont is going to have to answer to her own backbenches is why, seven years into this SNP government, we are still ahead in the polls.

"On today's performance, Johann Lamont is staying in opposition. But I tell you something else, on today's performance she ain't even fit to be in opposition, let alone government!"

Her recuperating backbenches were dutifully frenzied, Labour's notably silent.

The Deputy PO reminded MSPs of "Rule 7.3 of Standing Orders" - to conduct themselves in a "courteous, respectful and orderly manner".

It was the biggest hollow laugh of the day.