"If we're going to prove I was in the room and I'm going to help you, I'd better put on my lab coat," says Malcolm Rose, analytical chemist, author of books on mass spectrometry and inventor of the popular Traces series of teen crime novels, launched this year.
There is a gasp at the coat's red splotches, which he avers with a twinkle, are blood spots from an accident he had to stop and analyse en route to the Lord Grey School, Bletchley, today. Seriously, though, these were just felt pen stains. But how can forensic scientists help with crime detection? And for how long has this young volunteer been left as a "dead body" on the classroom floor? The answer, involving rigor mortis ("He'll be cooling down soon," calls out one Year 9 girl), insects and decomposition is, says Malcolm Rose, an example of the "apparently awful way in which nature recycles elements of the body". It's also a striking way to illuminate some key scientific concepts on a wet Friday afternoon.
When we move around the world, what traces do we leave behind us? And how do scientists track them? As Malcolm Rose goes through the evidence he has left behind in his 20-minutes' worth of talking about being an author, eyes widen and hands shoot up. "When is a glass of water more than a glass? When is it a clue?" "Sir, you left your saliva on the glass." "Which means?"
Three little letters for a massive concept, but the children seem to grasp it - sequencing, the stuff of life, chemical markers - just as they go beyond the notion of fibres snagged from trousers and focus on the differences between polymers and natural fibres in clothing. And then there is the cough and sneeze.
They get those, but are suitably revulsed to hear that a cough travels at 60mph and a sneeze at 100mph: speeding snot, yuck! A theatrical wipe of the hand and splatter of sweat from a heated brow has been noted by the eagle-eyed bunch in the front row, who are even more revulsed to learn about possible toilet clues and intimate DNA material.
Then there's that muddy shoeprint. The pattern and shape says a lot about Malcolm's footwear and analysis of the soil can reveal where he's been.
"Near the end, you scratched your head." "So?" "You'll have left some hairs and skin." "Well spotted. And very polite. You didn't call me an old balding bloke with dandruff." That's more DNA left behind in the classroom.
This is problem-solving at its most technical, with a plea to work out how to salvage writing impressions from an apparently blank pad. By scraping graphite from a pencil over the pad and brushing lightly, words can be read - do it yourself at home.
One of the most interesting parts of the workshop for science teachers comes with a discussion of fingerprinting. Fingerprints have, according to research printed in New Scientist, never been scientifically validated (for accuracy). Their rate of error has never been determined in the 100 years in which they have been used, though individuals have had judgments reversed when fingerprint evidence has been shown to be distorted or partial. As Malcolm Rose points out, partial prints are inevitable. A glass, for instance, is curved yet the pads on fingers are more or less flat. Most prints on curved surfaces, therefore, are somewhat partial.
Which leads very nicely, considers Philip Owens, head of science at Lord Grey, to a consideration of scientific error and how accounting for error is integral to scientific investigation and method.
Another common bugbear in science is communication. The Traces books, set in a parallel England, feature a robot, Malc (Mobile Aid to Law and Crime) who cannot understand figurative language. So if you tell him "I smell a rat" he'll reply: "There are no odours indicative of vermin."
Getting pupils to discuss unambiguous expression is very valuable. More valuable is reinforcing that basic truth that humans are by nature scientists and that "science is applied curiosity". Or, as Year 9 at Lord Grey put it, that was "dead good".
* Malcolm Rose's third book in the Traces series is Roll Call, Kingfisher Books pound;5.99.
Email: email@example.com www.malcolmrose.co.uk