At the moment that Formali-Kai detected whatever it was moving inside the Cathedral, it had produced a couple of shinily mean-looking knife missiles which shot out from some concealed openings in its carapace and accelerated hard in the direction their sensors had indicated. The drone zoomed off after its knife missiles, its luminescent sensing band visible long after the rest of the machine had disappeared.
"Stay here," Valbada told Histoker, "See what the suit's sensors make of that mark. I’ll track down this intruder, whatever it is."
Histoker had just enough time to say "sure" before Valbada's suit also disappeared into the forbidding gloom of the Cathedral. He shrugged - a movement comfortably accommodated by the suit itself - then focussed all of the suit's sensors on the little scratch on the wall. The readouts were confusing, contradictory, to say the least. It was difficult to get any consistent view of the depth of the mark, or any indication of the direction from which the object or energy discharge, whatever it was, had struck.
"Suit," he said, "What's the density of the material making up this wall."
"It has never been possible to determine precisely the density of the material which makes up the objects in the Chaosarium," the suit replied primly, "The exact result depends on whether gravimetric, stochastic or volumetric methods are used."
"So it is exotic material?"
"Yes. And by any of the measures, it is extremely dense. The energy required to make this mark is only moderately high, although it is hard to estimate exactly the amount."
"An approximate value of the energy for the mark, then?"
"It is about three-point-one times eight-to-the-ten joules," the suit replied immediately.
Histoker was not really impressed. This amount of energy was equivalent to, for example, the single-bolt mode of an old-fashioned peace-rated handgun, and therefore of course miniscule compared almost any modern Culture weaponry; the kind of impact energy that the suit's weapons - or any of the drone's systems - could deliver would outclass the blow to the walls by several orders of magnitude.
"So, just a small blow then," he said, adding, "But was it enough to perturb the motion of this sphere?"
The suit was strangely silent for a moment. Histoker, who had been brought up surrounded by very smart machines, was entirely used to getting an answer to any question immediately - unless, of course, the machine in question was being snarky, whimsical or otherwise trying to make a point.
"Suit? Did you hear me?"
"I did. My apologies. The answer is, I don't know. The amount of energy which appears to have been used is right at the level where the chaotic motion of the Cathedral makes modelling the result intractable, at least with the resources I have available to me."
The suit sensors pinged politely and an overlay screen lit up displaying four coloured motes, helpfully identified by the suit as Valbada in her suit, the drone Formali-Kai and its accompanying knife missiles. Despite the overlay, Histoker could not make out the returning companions in the gloom. As he watched, three of the markers converged and coalesced: the knife missiles returning to their customary resting-place within the drone.
Seconds later, drone and suit slammed to a stop next to Histoker.
"We lost it," Valbada said gloomily, "Whatever it was."
"Indeed," the drone added drily, "It must be equiv-tech or something very close, if it was able to shake us off so easily. Or get in here without us noticing it."
Histoker was just relaying what the suit had said about the impact energy that formed the scar when the scream of a high-urgency alarm cut through the discussion. His suit whipped around and brought up a mirror field far faster than he could have reacted alone, even with the aid of SC-grade implants and enhancements which were even now cutting in.
"Incoming," Formali-Kai's calm voice sounded in his ears, "We are under attack; Effector intrusion attempts and CREWS fire."
The suit popped up targeting overlays and damage report screens, the latter showing optical and UV coherent radiation being effectively blocked by the fields, while the laser carbines embedded in both the suit's forearm sections armed themselves and indicated they were ready to discharge at an instant's notice.
"I'm trying Effector countermeasures," the drone added, "Want to get the thing disabled quickly. Not working at the moment."
Another damage control readout in Histoker's suit indicated that some minor subsystems and capabilities were under threat from Effector intrusions, while the mirror field controls reported that the incoming CREWS fire had increased by three orders of magnitude and that the now-conical fields were at their limit of what could be deflected without serious suit damage.
"Shoot the thing down!" Valbada shouted, "Shoot it now!"
"Agree," the drone responded, "Fire now. Maximum yield."
Histoker released the restraints on the laser carbines, which immediately fired an alternating series of heavy-duty bolts, both arms shuddering and jittering as the suit made fine adjustments to the alignments of the firearms. Nearby, he could see that Valbada's suit was discharging plasma rounds, a staccato fusillade of soundless flashes in the near-vacuum within the Cathedral. The drone too was firing rapidly, although exactly what weapon systems it was using was not immediately clear.
The target of this assault was visible only as a scintillating point in the distance that swooped and swerved as it dodged and deflected the many munitions aimed at it. Neither laser bolts or plasma rounds were detectable against the starfield visible through one of the many large openings in the surface of the Cathedral.
Without warning, the mote exploded into an expanding fireball as one or more of the shots from the suits and the drone got through its defences. There were a couple of secondary explosions forming short-lived bright as sub-munitions detonated. The suits’ carbines and plasma tubes stuttered to a halt as sensors confirmed the complete obliteration of whatever device - it was far too small to be a human in a suit - had attacked them.
"We got it!" Histoker said, his voice shaky with relief, "Everybody okay?".
"I'm fine," Valbada replied, also sounding relieved, "But what the fuck was that thing?"
"Fine here too," the drone said, "I'm not sure what it was. We need to take a closer look at whatever's left."
Histoker spent a few moments backing down and turning off the various SC bodily enhancements which had kicked in the instant that they had been attacked, while examining the damage-report readouts closely. The suit reported that it had suffered no significant permanent damage, although it had been touch-and-go for a few moments: if the attacking device had not been disabled within the next few seconds, things would have gone very badly indeed. He then edged forward cautiously, following Valbada and Formali-Kai, and asked the suit's AI to focus every available sensor on the residue of the engagement, as well as reviewing the radiation signature from the device's destruction and the cloud of rapidly expanding and cooling plasma and a host of decaying exotic particles which was all that remained from the explosion.
"It looks like we triggered a matter-antimatter annihilation event," he said, as he caught up with the others, "So the device was powered by an AM reactor."
"Yes. AM residue in the secondary explosions, too. If I didn't know better," Valbada said slowly, "I would think that it was a Culture device."
"Agree," the drone said immediately, "Something like an SC-grade knife missile, a reasonably modern one in full-on no-holes-barred attack mode, could have pulled off an engagement with this profile."
"Formali-Kai", Valbada asked firmly, "Aren't drones of your model normally equipped with a total of three knife missiles?"
There was a long pause; long enough for a smart machine like Formali-Kai to perform a huge amount of cogitation. Histoker twisted his suit to glance at Valbada; she looked glum through the faceplate.
"I believe I owe everybody an apology," the drone said sombrely, "We've just been attacked by one of my own knife missiles."