be in the dark形容“蒙在鼓里，浑然不知”，keep sb in the dark形容“将事隐瞒不使人知道”。

We were kept completely in the dark about his plan to sell the company.

对他计划将公司出售一事，我们一直蒙在鼓里。

来看“隐瞒”的英语表达：

①conceal

Is there something you're concealing from me?

你是不是有事瞒着我？

②hold out on sb

Don't hold out on me - I need to know who did it.

别瞒着我——我需要知道是谁做的。

③keep back

I suspect she's keeping something back.

我怀疑她有所隐瞒。

④pull the wool over sb's eyes

We can see through all your tricks and schemes, so you needn't think you can pull the wool over our eyes.

我们能够识破你所有的阴谋诡计，所以不要以为你能蒙骗我们。