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ulterior motive; plot; scheme
complicated circumstances; intricacies
彼の魂胆は見え透いている。
His ulterior motive is transparent.
一体どんな魂胆があるのか疑わしい。
I'm suspicious of what kind of scheme he has in mind.
その申し出の裏に魂胆がありそうだ。
There seems to be an ulterior motive behind that offer.