Oneword: Lantern

Watson ran his hand along the cave wall, shuddering as it quickly became coated in a damp slime. He could hardly see where his feet were going, or even what he was stepping on, as the light from the lantern which Holmes carried was so dim, and so much further ahead in the underground passage. "Holmes!" he hissed, surprised by how loudly his voiceless call echoed in the tunnel, "Wait the bloody hell up! Your target is dead, remember? He won't be going anywhere any time soon!"

Holmes paused and lit a cigarette from the stout, oil-fed flame, and smoked it impatiently while Watson struggled to keep up. "If the rats destroy any evidence before we get to it, I'm blaming you," he muttered, puffing just once or twice before stubbing the end out on the damp wall. Wouldn't do to flood the cavern with smoke, after all, what with visual conditions as compromised as they already were.

He offered an arm as Watson finally reached him, which the shorter man gladly took, ensuring a safe journey through these wretched caves as they followed their map of clues.