Chapman looked at Ashley, then at Jack, then nodded to the other officers, who released him. Ashley didn’t wait a second, darting through the cordon with Jack close behind.

“Thanks,” muttered Jack as they hurried into the gloom of the underground car park.

“Never mind that,” replied Ashley. “What are we looking for?”

“Seven cucumbers, each one the size of a small torpedo. They’ll be in a red van.”

They found it on the lower level. Jack looked in the driver’s window. There were several green coveralls dumped on the passenger seat. The key wasn’t in the ignition. He cursed, went round to the back and was just about to open the rear doors when he realized that the van was radiating heat. He touched the door handle with a saliva-tipped fingertip, and it hissed malevolently at him.

“Shit,” he said. “It’s begun.”

He wrapped a handkerchief around his hand and threw open the doors, ducking to avoid the hot waft of air that rolled out. The interior of the van was filled with the giant cucumbers Jack had last seen in Hardy Fuchsia’s greenhouse, with the uppermost cucumber resting on a digital scale. A tube from a bottle was leading into the giant vegetable, with a time switch metering the weight-gaining contents. The digital scale read 49.997 kilos, and already the cucumber’s smooth skin was turning from green to a dark orange and giving out large quantities of heat—the paint on the van’s sides was starting to blister.

They both stared at it blankly for a few seconds.

“I don’t know the first thing about disarming thermocuclear devices,” admitted Jack, the fear rising in his voice. Bomb disposal was usually a case of cutting the blue wire, but there weren’t any wires in sight—and the reaction had already started.

“Well, don’t look at me,” retorted Ashley, going a deeper shade of blue.

“I thought you were meant to be an advanced alien race or something?”

“We are,” replied Ashley indignantly. “I’m just not that good on low-tech stuff. How are you on steam engines and windmills?”

“Okay, okay—let’s not argue about this.”

Jack moved closer and winced with the heat. The cucumber was starting to glow from within, and lighter patches the size of small coins were appearing on its skin.

“We need a moderator,” said Ashley, having just worked out the principles of nuclear-fusion theory from scratch. “The light hydrogen isotopes of deuterium and tritium are combining to form a heavy helium atom and a spare neutron. It’s the spare neutron that continues the reaction—soak up that and this cucumber is just a large and very hot vegetable.”

“So what do we need?” asked Jack, not having understood a word.

“Half a ton of graphite.”

“Graphite? Where the hell are we going to get that from? A million pencils?”

“Or just plain water.”

Jack looked around desperately for a few fire buckets or something and then took an involuntary step back as the reaction grew even hotter. The light patches on the cucumber’s skin formed into dimples and then collapsed inward into holes, which projected shafts of pure white light from the rapidly overheating core. The same effect was beginning to start on the other cucumbers. Even though they were under the necessary fifty kilos, the single critical cucumber was bringing them all up to ignition.

“I’ll find some,” said Jack, making a step to go. But Ashley stopped him.

“It’s already full of holes,” he said. “There’s no time. Do you have your penknife?”

Jack rummaged in his pocket and drew it out, his hands shaking as he snapped open the large blade.

“I have a liquid core that will do just as well—only take care. As well as being an excellent moderator, it’s also a powerful molecular acid—don’t get it on yourself.”

Ashley closed his eyes and pulled open his jacket to reveal his taut, transparent skin.

“I need a breach in my membrane, sir. You’ve got to stab me.”

Jack stared at him. They took another step back as the heat intensified. The paint had caught fire on the outside of the van.

“I can’t, Ash.”

“Jack,” said Ashley as he placed a single sucker digit on Jack’s forehead, “you must do this.”

“Of course,” replied Jack as the power of Ashley’s infinitely superior intellect pushed aside the barriers of illogical emotional reasoning. “It’s all so very clear.”

And he plunged the knife into the alien’s abdomen without delay. Ashley had tensed himself, and Jack pulled out the knife.

“Stand back, sir.”

The cucumber had started to break down further, and the light and heat were now so intense that Jack had to shield his eyes. Then an arc of soft blue liquid shot from the wound on Ashley’s chest, and with a rapid flickering and a tearing noise, the light in the cucumber began to flash and dance as Ashley’s liquid insides reacted with the subatomic tumult within the cucumber’s core. The light faltered, brightened, flashed, then went out, and all the cucumbers rapidly began to melt under the destructive power of Ashley’s aqueous innards. But it didn’t stop there. The neutron-absorbing cascade of rambosia vitae dissolved not only the cucumbers but the chassis of the van containing them and the concrete floor beneath, making a strange hissing and bubbling noise and giving off a smell like toffee apples.

Ashley had squeezed every last drop from himself and finally fell back empty like a deflated balloon, his once-snug uniform falling off him. Jack cradled Ashley’s now-flattened head in his arms, but he wasn’t yet dead. His eyes flickered open.

“My mind is going,” he said in a soft voice. “I can feel it. All that I am. Tell… tell… What was her name again?”

“Mary?”

“Right. Tell Mary I… would pluck the stars from the sky… 100… her… 10010101… 10… 1.”

“Tell her yourself, Ash. Ash?”

But it was no good. Ashley had gone. The liquid center that had so successfully quenched the thermocuclear device also carried the memories and experience that made him the alien that he was. Without them he was nothing but a deflated blue bag. In a very real sense, he had forgotten himself for the benefit of others.

The van collapsed in the middle as the rambosia vitae ate through the chassis. There was now a smoking hole in the concrete floor revealing the next level down, and a car that had the misfortune to be directly below was also being dissolved, albeit a bit more slowly as Ash’s vitae ran out of power.

“Ash,” said Jack to the light blue membrane that was draped across his hands like a silk scarf, “I’ll get them, don’t you worry.”

The small alien had traveled 18 light-years to find out more about our sitcoms and ended up saving half of Reading. It was an odd state of affairs, even by Ashley’s standards, but Jack had no time to dwell upon such matters—the inquiry had not yet run its course. NS-4 and QuangTech still had a lot to answer for, and the fourth bear was still out there somewhere. Jack looked up as he heard the sound of feet running down the entrance ramp.

The first on the scene was Briggs, with Copperfield and several other officers close behind. They stopped dead in their tracks when they saw Jack and the shriveled blue transparent bag that had once been Ashley.

“Where’s this ‘thermonuclear device,’ then?” asked Briggs.

“In the van,” replied Jack as the back axle finally dissolved to nothing and the Ford transit collapsed. They looked inside. It was empty, of course. The vitae had eaten through everything.

“It was there,” said Jack, “seven giant cucumbers about to achieve critical ‘cuclear’ ignition—but rendered harmless by Ashley’s memories.”

“I was right,” said Briggs. “You’re stark, staring mad.”

“I can explain. NS-4 and the Quangle-Wangle—”

“Drop the knife, Jack.”

Jack looked down. He was still holding the penknife.

“You killed the alien!” said someone at the back.