entertain dark schemes;harbour evil (/sinister) designs; have evil inten tions; have ulterior motives; in an agony of guilt;with evil intent (/purposes/misgivings) in one’s heart
❍ 至次日见了鸳鸯，自是脸上一红一白，百般过不去，心内怀着鬼胎，茶饭无心，起坐恍惚。(《红楼梦》541)The next day when she saw Yuanyang she turned red and white by turns in an agony of embarrassment and guilt. She lost her appetite and grew quite bemused.
❍ 王红眼～而来，又知道高学田是个火气大的人，怕把他弄急眼下，再抡起大扁担来，打乱自己的如意算盘，……(《高玉宝》39) Wang had come with an evil design. But he knew Gao’s temper-if driven too far he might strike back and spoil Wang’s scheme.
心怀鬼胎
cherish sinister motives;harbor evil intentions;have evil designs
心怀鬼胎xīn huái ɡuǐ tāi
鬼胎：比喻不可告人的事情或想法。指心中隐藏着不可告人的事情或想法。have ulterior motives, with evil intent, conceive mischief