Bosnia and Herzegovina, Brčko District, night.

No moonlight.

Only the flickering orange-red light reflected from burning buildings and the occasional trajectory of tracer rounds streaking across the night sky.

Lieutenant Colonel Milovan Kovach, Commander of the Serb Republic's "Special Police Force," crouched behind a broken wall, whispering into an encrypted satellite phone, his tone a mix of excitement and anxiety: "Yes, most of Brčko's eastern district is under control, but the Croatian ethnic militia is putting up a strong resistance near the refinery. We need more anti-tank weapons; they have a few old M-84 tanks."

A processed voice with a Spanish accent replied from the other end: "The second shipment is on its way, exchanging at the old tunnel of the E72 Highway. Remember, at three in the morning, wait only ten minutes. The 'Puma's' weak point is the rear engine compartment; don't let them flank."

Kovach licked his dry, cracked lips: "When will those 'observers' withdraw?"

"Mission completion means withdrawal. Do your job and ask no unnecessary questions." The call disconnected.

Kovach put away the phone, glancing at the two "consultants" in civilian clothing but displaying highly professional tactical moves in the nearby shadows. They were adjusting a portable device with an antenna, likely an electronic jammer. These people were not Serbians, Kovach was sure. Their equipment was too good, unnervingly good.

"Commander!"

A soldier with a face full of soot crawled over, "NATO planes! Southwest direction, sounds like 'Tornado' reconnaissance model!"

Kovach looked up, a faint hum of jet engines audible in the night sky. He pressed the intercom: "All units, take cover! Shut down unnecessary electronic devices! Air defense units on standby but do not fire! Repeat, do not fire!"

Firing would provide NATO a reason to intervene. This was the line the "consultants" repeatedly emphasized: create facts, but avoid footage of "mass atrocities."

In the distance, near the refinery, explosions intensified, seemingly the Croatian ethnic militia retaliating with mortars. Kovach cursed and ducked toward the command vehicle. The surprise attack had started smoothly but was sliding into a war of attrition. He needed the batch of anti-tank missiles, and more importantly, an "unexpected event" to break the deadlock.

...

At the same time, North Sea, Scottish Self-Defense Army exercise area, "Celtic Guardian" light frigate.

On the bridge, a short alarm sounded.

"Sonar contact! Unknown underwater target, bearing 270, distance 15 chains, depth 100 meters, moving slowly!" The sonar operator's voice was tense.

Commander Alasdair MacLean quickly approached the control console. The sound signal on the screen was blurry, seemingly specially processed, yet that extremely low mechanical noise characteristic... not a merchant ship, nor a common NATO submarine.

"Maintain tracking, passive sonar mode. Alert 'Seagull' and shore-based anti-submarine helicopters to standby."

MacLean ordered while glancing at Mexican Navy advisor Lieutenant Colonel Castro, standing in the corner of the bridge.

Lieutenant Colonel Castro showed no expression, only nodding slightly.

The exercise plan contained no provisions for "unknown submarine." This was an unplanned "guest."

"Commander, the target is accelerating! Changing course, heading right for the center of our ship formation! Speed... 8 knots, 10 knots, still increasing!" The sonar operator's voice raised by eight degrees.

"Active sonar pulse, prepare warning shots!" MacLean no longer hesitated. Whoever was coming, intruding into the live-fire exercise area was a provocation.

"Wait." Lieutenant Colonel Castro suddenly spoke, his English heavily accented. "Sound signature analysis complete. Match 87%... It's Sweden's 'Gotland'-class AIP submarine 'Halsing.' It's not supposed to be here."

"Swedes?" MacLean frowned. Sweden is a neutral country but cooperates closely with NATO. "What are they here for?"

"Perhaps 'observation,' perhaps... testing." Castro walked to the sonar screen, fingers swiftly tapping the keyboard to pull up data, "Last month, 'Halsing' participated in NATO joint anti-submarine exercises in the Norwegian Sea. Its stealth performance is excellent; this time, actively exposing itself... might be deliberate."

As if to verify his words, a calm voice with a Northern European English accent came over the public radio channel: "Scottish Navy formation, this is Royal Swedish Navy submarine 'Halsing.' Our vessel is undergoing routine training in international waters, with no intent to disrupt your exercise. To avoid misjudgment, requesting a safe passage to leave the area. Over."

Requesting to leave? Yet their course infiltrates the center of the formation? MacLean sensed something amiss.

"Give them a passage. Indicate bearing 190, depth maintained at 80 meters, speed not exceeding 5 knots." MacLean ordered while connecting the encrypted line to the exercise commander McTavish, "Officer, situation brief..."

...

Edinburgh, Holyrood Palace underground command center.

McTavish listened to MacLean's report, staring at the map showing the light representing the Swedish submarine.

"Swedes... neighbors to the Norwegians." He looked at Callum, "Has there been any leakage in our contacts with Norway?"

Callum shook his head: "Absolutely secure channels. But within the Norwegian government, it's not a solid front; pro-European and pro-American factions have been vying for power. If the United States or European Intelligence Department catches a whiff of anything..."

"It's a warning." Former SAS operative John McLean stared at the screen, "The Swedish submarine appearing here isn't a coincidence. They're showcasing capability: even if you have equipment from Mexico, we (or those behind us) can quietly reach under your nose. Simultaneously, they're testing our response and the level of intervention by the Mexican advisors."