The train hurtled through the tunnel like a long nail hurled into the dark, piercing the blackness with the metallic tang of rust and diesel. The car swayed violently; every jolt sent condensation spraying from the insulated crate onto the back of Samira's hand, chilling her to the bone. On the crate's metal latch, a red diode pulsed, the temperature reading flickering between 5.2°C and 4.8°C—like a second hand choking.
Ilyas slid down the carriage wall, his knuckles probing the darkness. His fingers found a cracked backup battery, exposed wires trailing like raw nerve endings. He clutched it to his chest like a failing heart.
"The bomb's wiring's under the crate," he breathed, the words barely audible. "Need three minutes. But light will bring them."
Samira didn't answer. She unzipped her hoodie and pressed the orange pinpoint below her collarbone against the crate's metal side. The light flared like a waking firefly, instantly spreading across the surface, weaving a fine mesh of warmth. The temperature reading jumped to 6.7°C; the red diode steadied into a solid green. Ilyas froze for a split second, then muttered a curse—wonder or terror, unclear.
"How long?" he asked.
"Until I can't," Samira's voice was ground flat by the wheels, yet steady.
The train jolted hard. Light flooded in from the tunnel's end. Footsteps approached outside the sliding door. Ilyas shoved the battery into Samira's arms and rolled into the shadows. The door scraped open a crack. A flashlight beam swept the crate, then pinned Samira's face. She squinted. A face mostly masked—only grey eyes visible, like unmelted ice in the tunnel.
"Temperature nominal," a flat, mechanical voice stated behind the mask. The beam shifted away. The door slammed shut. Darkness swallowed them again. The footsteps receded, leaving only a faint, low-frequency hum, like a machine calibrating a distant heartbeat.
Ilyas crawled back, thin copper wire stripped from the battery in his hand. "Keep the heat," he said, looping one end around Samira's wrist, the other into a spare port on the crate. "Let the current ride your skin. Don't let it reach your heart."
Samira nodded, biting her lip. As the wire touched her vein, a burning pain shot up her arm and into her chest, a fiery tongue licking backwards through her blood. The temperature jumped to 7.4°C. The orange light pulsed on the metal, reflecting off her pallid face. She heard her own heartbeat amplified through the wire, becoming the carriage's only light source.
The train burst from the tunnel. Moonlight sliced through louvered vents, cutting the crate, the wire, her face into silver slivers. Ilyas lay prone under the crate, a screwdriver flashing in his hand like a surgeon operating on the dark. Each metallic *tink* was punctuated by the crackle of a distant guard's radio.
"Wiring's trickier," Ilyas hissed. "They tied the negative to a heart-rate sensor—if your pulse drops below sixty, it thinks it's freezing."
Samira gave a rasping laugh. "Then let it listen to me."
She closed her eyes. She pictured Karim curled small within the thermal blanket: frost on his lashes, nose red with cold, murmuring her name in sleep. Her heartbeat surged—eighty, ninety, one hundred—the orange light in the wire pulsed with it, stretching into a glowing filament, bathing the entire car in a warm, ruddy glow.
Footsteps again, closer, faster. Ilyas snipped the final wire. The bomb's red diode died completely. He snapped his tools shut and twisted the crate's latch—*snick*, like closing someone's eyes.
The door was wrenched open. Three flashlight beams stabbed inward. Samira stood before the crate. The pinpoint on her chest winked out. Darkness reclaimed the car. The Grey Trench Coat stepped halfway in, his torch beam fixing on her face.
"Step back," he ordered.
Samira didn't move. She heard her heartbeat echo one last time through the copper wire: like the clack of wheels on rails, like the fading call of her name in Karim's dream, like the unyielding light at the tunnel's end. Then she reached down and ripped the wire from her wrist. Blood beaded, falling onto the metal floor with a soft *tap*.
The Grey Trench Coat raised his gun. The safety clicked off like ice cracking. At that precise instant, the train slammed into an emergency stop—a shriek of rending metal shredded the darkness. Everyone pitched forward. The insulated crate slid towards the end of the car. Its lid flew open with the force, revealing Karim's pale face within the thermal blanket, frost still on his lashes, but his eyes were open.
Samira lunged, gathering him into her arms. Heartbeat pressed against heartbeat. Warmth flowed into warmth. The Grey Trench Coat, thrown off balance, fired wild. The bullet sparked off the roof. Ilyas yanked the sliding door wide open. Frigid air rushed in, thick with the frost and stars of the open fields beyond the tunnel.
The train hadn't fully stopped. Samira jumped into the dark, Karim clutched tight. Her knees hit the gravel with a jarring crack; pain whited out her vision. But she heard the boy in her arms murmur, thick with sleep, "Sister… the light's too bright."
She looked up. The train's red tail lights shrank in the distance like two diminishing red beans, then vanished into the night. The wind of the open plain dried the tears on her face and extinguished the last echoes.
Only the heartbeat remained, a filament refusing to be extinguished, burning quietly in the dark.