"Are you ok?!" he yelled. The adrenaline was still pumping.

"No! Of course not! What happened?"

"Those men tried to steal your new samples. They must have followed us here."

She was shaking, Sam realised. He was surprised she wasn't already going into shock. He snapped on the heating and regretted it instantly as the warm damp air inside the car began to condense on the cold glass. He wiped it with his palm and roughly searched for the right airflow while trying to keep one eye on the road ahead and one on the road behind.

Lyn turned round in her seat, flopped into it and fumbled for the seatbelt.

Sam turned onto the main road without slowing down and the car lifted onto three wheels. He crunched through the gears, ignored the screaming engine and flattened the pedal.

The windows were starting to clear. Behind them two familiar headlights were growing larger.

Lyn was shaking her head.

"They didn't know what samples I was taking."

"Lyn, it makes sense. This must be related to the attack on the lab. They want your DNA. Why?"

"I don't know! I don't know why anyone would want it, ok? If they asked me I would give it to them."

Sam glanced at the back seat where the both transport bags had somehow ended up.

"If that's what they want we can drop the bags. Maybe they'll stop and take them."

"I didn't bring my own DNA out. We don't need that back in London."

"They don't know that!" yelled Sam. "Do it!"

He pulled across the lanes to overtake another vehicle.

Lyn stretched between the seats and snatched at the two bags.

"Stay this side of the road and slow down so they see it," she said.

Sam eased off the pedal and dropped the car into neutral so they would coast at sixty miles an hour. Behind them the Mercedes edged closer, and Lyn flung the bags through the window.

The Mercedes didn't even slow down.

Sam shifted up the gears and accelerated again but this time furious they had lost their lead.

"They didn't stop," she cried. "Why? The DNA might be in there. They don't know it isn't."

Sam realised the truth before Lyn.

"No, they don't," he said grimly and looked her in the eye. "But they do know it's in here."