There was something up with the Astronomy Club. The entire membership—consisting of four teenagers—had been holed up in Observatory's empty lecture room for over an hour now and were conducting a furious conversation in lowered voices. Linua paused with her broom outside the door and listened.

"…in disguise!" one of them said. "It was the same guy!"

One of the other boys asked a question, which was answered by the girl.

"…at the Observatory!"

There was babble as they all talked over each other. The girl called them to order, telling them to shut up and listen. The first boy spoke again, but it sounded like he'd moved further away from the door and Linua couldn't hear what he said.

She wondered what they were talking about.

If Alnan had been here, he and Linua could have turned the mystery into a guessing game. But he was on his two weeks of annual leave, and the temporary janitor the agency had sent to replace him was surly and irritable, and had as little desire to spend an evening in Linua's company as she did in his.

One of the younger boys was speaking.

"…have to do something!"

"We tried to tell Dad," the first boy replied.

"But he thought we were making it up." That was the girl.

"So we've got a plan…" the first boy's voice faded away and then came back. "…and to do that we need to get into the vault."

Another outbreak of voices, all protesting at how difficult that would be.

Linua wondered why they wanted to get into the vault. It was a fancy name for an old cellar that had been converted into a storage room for all the artefacts that weren't displayed in the museum. Nearly everything in the museum had been collected by Sir Lee Seng, who had caused the original Observatory to be built a century ago.

Sir Lee Seng had been a prominent Shang citizen whose obsession with the history of astronomy was, fortunately for him, rivalled only by his vast wealth. However, his lack of trust in lesser, more barbaric cultures—i.e. anyone not Shang—to preserve their own astronomical artefacts with the appropriate level of reverence had impelled him to gather up as many of such artefacts as he could get his hands on by any means necessary. He had then carefully preserved them in the dusty old vault situated below the Observatory, where they lay hidden from public view for decades at a time, and were only ever seen by a handful of astronomers.

A tiny portion of Sir Lee's collection was displayed in the museum, but Linua knew there must be huge amounts of old and forgotten things in the vault—astrolabes, orreries, books, scrolls, tablets, zodiacs, sky disks, artefacts of astrology and divination, the first precursors to telescopes, and probably a great deal more.

And now the Astronomy Club was planning to break in. They were lucky that the staff at the Observatory weren't the noticing sort of adults. Or rather, it was true that they noticed things, but only about astronomy, and certainly not about teenagers.

Linua's grandmother, had she been made aware of the existence of the Astronomy Club, would have insisted that Linua join it. Linua was fourteen, after all, and therefore of a similar age to the members. Linua wouldn't have minded making friends, but when there had been other kids her age at the Observatory before, the moment they found out about Linua's parents, her family or her education—take your pick—they acted as if she was weird. Which was probably true. Both sides of Linua's family had developed such galloping great levels of 'we are not like other people' that Linua had never stood any chance of turning out suitably normal.

Anyway, Linua didn't want to have anything more to do with astronomy. One of the benefits of hanging around with Alnan instead of the astronomers was that he had no interest in the subject whatsoever. She missed him already and he'd only been on holiday for a couple of days.

The Astronomy Club plotting session was still in progress.

"I'll get the equipment," one of the younger boys said. "…can help me set it up."

The older boy said something about stealing, then the girl spoke sharply.

Were the Astronomy Club members planning to steal something from the vault? Or did they think someone else had stolen something?

The museum and the vault were situated in the oldest part of the Observatory which still had the original wooden doors bound with iron. Alnan's set of keys could open the museum, but the key to the vault itself was kept by the trustees—it wasn't even on the premises. Was the Astronomy Club planning to steal the key, or did they think they could pick the lock? Linua thought about the vault door lock for a moment. Like the doors, it was the original lock installed by Sir Lee, a massive block constructed from a slab of solid iron, but the keyhole was so big you could stick your finger in it. Presumably a century ago it would have been considered the cutting edge in locking mechanisms, but now that Linua thought about it, it might not stand up to the determined efforts of a bunch of teenagers.

What would they be after that was inside the vault?

The museum was Linua's second favourite part of the Observatory, the first being Alnan's little cubby hole where he brewed his tea and kept his tin of biscuits. The museum made the Universe seem like some grand mystery full of enticing secrets just waiting to be discovered. The truth was that a great deal of astronomical studies were obsessed instead with the search for the ancient lost mothership of Lord Nimras. Those kinds of research projects were the ones that got all the prestige, the generous grants, and prime time on the biggest, newest telescopes. People who wanted to study actual stellar phenomena, like, for example, the creation of the Universe and everything since, were relegated to smaller, less important telescopes like the one at the Observatory.

If Linua's parents hadn't let themselves get caught up in the search for the mothership Linua would still have a real family, instead of being shunted between two sets of extremely demanding and eccentric relatives.

She repressed the familiar pang at the thought and bent her head to listen more closely at the door, then realised there was a clatter of approaching footsteps from the other side. The Astronomy Club had finished their secret conference.

Linua quickly took a few silent paces down the corridor, where she turned around and began pushing the broom towards the lecture room just as the Astronomy Club burst out of the door. The front ones checked with a guilty start as they saw her—and wouldn't that have immediately made her suspicious, even if she hadn't already known something was up.

The front member—a tall, commanding girl of about fifteen or so—said, "Oh, uh, hi … uh…" clearly unable to recall Linua's name. She staggered forward a step as the next member behind her pushed her forward. He was the one with a shock of red hair sticking up in all directions, and the air of someone desperate to be noticed.

"Hi … uh, Lee, is it?" he said. "We were just, um…"

"…having a meeting," said the third member, peering around the other two. He was younger, about thirteen, and one of those children destined to be small, plump and more intelligent than anyone else for the rest of his life.

"…about how we're going to take pictures of the conjunction of Ishtar and Marduk," the red-headed boy finished, naming two of the outer planets in the solar system.

The leader of the Astronomy Club, a boy as tall and bossy as his sister, pushed everyone forward until they were all standing in the corridor. He gave an impatient sigh.

"She doesn't need to know any of that," he said irritably, trying to herd them onwards.

He was quite right, if somewhat rude. It was the first time the club members had ever offered Linua an explanation for anything they had done. They had never even greeted her before. Mostly they had just run past her as if she was part of the furniture, which was fine with Linua. She had found that holding a broom was a bit like wearing a cloak of invisibility.

Also, the Astronomy Club seemed to know as much about astronomy as they did about subterfuge.

"The conjunction of Ishtar and Marduk was last week," Linua said.

They all stopped and gaped at her with open mouths.

"How did you...?" the tall, commanding girl began.

At the same time plump boy slapped his forehead.

"Oh gosh, we must have got the dates wrong! What clods!"

Linua realised, belatedly, that of course they had known the conjunction was last week. In fact, the Astronomy Club had met on Threesday instead of Twosday so they could observe it. What they hadn't expected was for Linua to know that. They all stared at each other for a moment.

"Have you finished with the lecture room?" Linua asked. "I need to sweep it."

They jolted into action, and hustled past her in a chorus of yesses and sorries. As they traipsed down the corridor one of them began "Do you think she…" and was frantically shushed by one of the others.

Linua went into the lecture room. She emptied the wastepaper bin, and wiped that afternoon's lecture off the blackboard, where Professor Gwynfred had been teaching the Virial Theorem. The professor thought that learning should be fun and he'd drawn little cartoon figures to represent the various parameters of the equation—a little superhero flexing his muscles to denote mass, and a squashed fruit to represent the gravitational constant.

Linua wished she'd had someone like Professor Gwynfred to teach her maths and physics and everything else Grandmother thought Linua should know. Mdm Patoni was nice, and a very thorough tutor, but she had been at the back of the line when a sense of humour was being handed out, and the ancestor spirits had evidently run out of any long before it had got to Mdm Patoni's turn.

Linua swept around the room methodically, and thought some more about the Astronomy Club. There was definitely something going on, but she couldn't tell exactly what from the short scraps of conversation she had overheard, except that it was something to do with a theft, and the Astronomy Club wanted to break into the vault.

Once the cleaning was finished, curiosity would have propelled Linua towards the vault door, but unfortunately Dr Aedan spotted her lingering in the corridor.

"Linua! There you are! I need your help!"