Mister M, a silver tabby with a serious face and an even more serious tail, sat on top of the box and looked down at his two agents.

Shadow, the black cat, sat very straight.

Marmalade, the fluffy ginger cat, was washing one paw and pretending he was listening all the time.

“Agents,” said Mister M, “we have a situation.”

Shadow’s ears pricked.

Marmalade stopped washing. “Is it food?”

Mister M narrowed his eyes.

“That,” he said, “is exactly what we must find out.”

Across the street, the baker had come out of his shop and was looking up and down the road. Usually, at this time every Tuesday, the fish van arrived and parked beside the bakery.

But today there was no fish van.

No engine rumble.

No open back doors.

No wonderful smell drifting across the street.

Marmalade looked concerned.

“The fish van is missing,” said Mister M.

Shadow’s whiskers twitched. “Suspicious.”

“VERY suspicious,” said Marmalade. “Very suspicious.”

Mister M nodded.

“Shadow, follow the baker. Find out what he knows. And make sure you’re not spotted.”

Shadow rose at once.

“I am a shadow,” he said. “I am never spotted.”

He slipped out from beneath the lean-to and padded across the street.

The baker walked towards the corner, still looking for the van. Shadow followed six steps behind him, keeping low.

The baker stopped.

Shadow stopped.

The baker turned around.

Shadow froze beside a flowerpot.

The baker looked at him.

I wonder why that black cat is following me, thought the baker.

Shadow remained perfectly still.

Then the baker shrugged and carried on walking.

Shadow followed.

Back at headquarters, Marmalade was staring along the road.

“I should investigate the missing fish,” he said.

“You are to remain here,” said Mister M.

“Yes,” said Marmalade. “But if the fish is missing, someone should check any suspicious food that appears.”

“There is no food.”

“That makes it more suspicious.”

Before Mister M could reply, the fish van finally turned into the street.

It came slowly round the corner and stopped outside the bakery. The back doors opened, and the smell rolled out.

Marmalade stood up at once.

“Evidence,” he said.

“Do not touch the evidence,” said Mister M.

But Marmalade was already crossing the street.

The fishmonger climbed down from the van and spoke to the baker.

“Sorry I’m late,” he said. “One of the crates tipped over. Had to stop and sort it out.”

Marmalade sat beside the nearest crate and sniffed deeply.

The fishmonger looked down.

“Well, hello there,” he said. “You checking the delivery?”

Marmalade looked up at him with great dignity.

The fishmonger laughed and placed two small fishes on a scrap of paper.

“For quality control,” he said.

Marmalade sniffed the fish.

"Ah! Two pieces of evidence," he thought.

Then he ate one fish.

He sat still for a moment, thinking carefully.

Then, after a brief and very serious pause, he picked up the second fish and carried it carefully back across the road to headquarters.

When Shadow returned, Mister M was still on top of the carrot box. Marmalade had placed the remaining fish neatly in front of him.

“Report,” said Mister M.

Shadow sat very straight. “The baker was observed. The fish van arrived late because of a tipped crate.”

Across the road, the baker waved at him.

Shadow gave a small nod.

“I’m pretty certain I wasn’t spotted.”

Mister M looked down at the fish.

“And your report, Marmalade?”

Marmalade sat beside the evidence.

“Suspicious,” he said.

Mister M considered the fish for a moment, then lowered his head and took a small, thoughtful bite.

Shadow stepped forward at once and took his share.

For several seconds, all three agents considered the evidence in silence.

“Well?” said Mister M.

Marmalade licked his whiskers. “Very suspicious.”

Mister M gave a slow nod.

“Agreed,” he said. “Further investigation will be required next Tuesday.”

For several quiet moments, all three agents shared the spoils of Marmalade’s endeavours.

Then, inside the old lean-to, opposite the bakery, the agents of C.A.T. settled down for a well-earned rest.

To anyone passing by, they looked like three ordinary street cats.

Which, of course, was exactly what they wanted people to think.