救不得你了 I Cannot Save You
那怪厲聲高叫道：「師兄，還他唐僧，救我命也。」那道士從裡邊跑出道：「妹妹，我要吃唐僧哩，救不得你了。」那怪厉声高叫道：「师兄，还他唐僧，救我命也。」那道士从里边跑出道：「妹妹，我要吃唐僧哩，救不得你了。」
逐句解 Line by line
The monsters cried out shrilly, "Elder brother! Give him back his Tang Monk and save our lives!"
還他唐僧 — give him back the Tang Monk — takes 還 as huán again. 厲聲, a harsh or piercing voice, is the same phrase used of Tripitaka hailing the Daoist from the courtyard 2,860 characters earlier, when this was still a story about manners.
The Daoist came running out from inside. "Sisters — I mean to eat the Tang Monk. I cannot save you."
救不得 is the potential negative, and the 得 drops to de because the character in front of 不 is a full verb, 救, to save. That is the rule: V-plus-bu-plus-de means cannot manage to. This chapter has eight of them and every single one turns this way.
Eleven characters and the alliance collapses. They ask him to trade the monk for their lives; he says he wants to eat the monk; therefore he cannot save them. The logic is stated as a simple consequence, which is what makes it appalling.
It also settles what has been ambiguous since the back-room scene. He did not poison four travellers out of loyalty to his fellow students. He agreed to it, listened to their grievance, promised to deal with it — and the moment the two aims separate, he takes the monk and lets the sisters go. 同窗之雅, the bond of the same window, was worth exactly as much as it cost him.
And 妹妹 — sisters — is still how he addresses them while saying it. The register never breaks. This chapter's particular cruelty is that nobody in it is ever impolite while doing anything terrible.