黑風山妖 The Fiend of Black Wind Mountain
不期火起之時，驚動了一山獸怪。這觀音院正南二十里遠近，有座黑風山，山中有一個黑風洞，洞中有一個妖精，正在睡醒翻身。只見那窗間透亮，只道是天明。起來看時，卻是正北下的火光晃亮。妖精大驚道：「呀！這必是觀音院裡失了火。這些和尚好不小心。我看時，與他救一救來。」不期火起之时，惊动了一山兽怪。这观音院正南二十里远近，有座黑风山，山中有一个黑风洞，洞中有一个妖精，正在睡醒翻身。只见那窗间透亮，只道是天明。起来看时，却是正北下的火光晃亮。妖精大惊道：「呀！这必是观音院里失了火。这些和尚好不小心。我看时，与他救一救来。」
逐句解 Line by line
It happened that when the fire arose, it startled a beast-spirit of the mountains.
不期 is "not looked for" — the storyteller's way of bringing in a consequence nobody in the scene intended. 獸怪 is a beast that has become a spirit through long practice. He will turn out to be a black bear.
Some twenty lǐ due south of this Guanyin Monastery there stands a Black Wind Mountain,
正南二十里: due south, twenty lǐ. The distance is given exactly because it is going to be argued over — Sanzang will object that twenty lǐ is too far for anyone to have seen the fire, and Wukong will answer that the light carried two hundred. Worth noting that the prior, when he names the same mountain near the end of the chapter, places it 正東南, south-east. The 世德堂本 says both, and the divergence is left standing here rather than tidied away.
and in the mountain there is a Black Wind Cave, and in the cave a fiend, who was just then waking and turning over.
Mountain, then cave within the mountain, then fiend within the cave: nesting the places one inside another is the standard formula for bringing on a demon, and any reader who has come this far knows exactly what it announces. The chapter title promised him before the first word of the story was told.
He saw a light coming through the window and took it for daybreak. Rising to look, he found it was a glare of fire in the north.
只道是天明: "took it for daybreak." Of every being within twenty lǐ of the Guanyin cloister, the one who mistakes the fire for the dawn is the monster.
The fiend started up. "Ah! This must be a fire in the Guanyin Monastery. How careless those monks are!
好不小心 is "how very careless" — the 不 here intensifies rather than negates, a trap for the unwary reader. A demon of Black Wind Mountain is tutting at the fire safety of a Buddhist monastery.
"I will go and see, and lend them a hand to put it out."
與他救一救來: "I will go and help them save it." He means it, too. The one creature in this chapter who runs toward a burning monastery intending to help is the fiend — and the running is what destroys him.
The chapter's second half opens with a joke so quiet it is easy to miss. A monster wakes in a cave, sees the sky red, thinks it is morning, and then works out that the Guanyin Monastery is on fire. His first thought — his immediate, unreflecting thought — is that the monks have been careless and that he had better go and help. 我看時，與他救一救來. Two hundred and thirty monks have just tried to burn two men alive for a robe, and the bear-spirit of Black Wind Mountain is putting on his cloud to run to their aid.
The next passage takes the joke back with both hands, and Wú Chéng'ēn plainly intends it to. But the sequence matters. The demon arrives as a neighbour, on good terms with the abbot — the two of them discuss doctrine together, as we learn later — and moved by exactly the reflex the monastery could not manage. He turns thief only once he has seen the cassock. Which is to say he falls in the identical manner, and by the identical light, as the old man who set his own house on fire an hour earlier. The cassock does not sort monks from monsters. It shows each of them what he is, and it does not take long about it.