to have a group of people, especially an audience, giving you their full attention and responding enthusiastically to everything you say or do
A cursory look at the audience shows that she's got them in the palm of her hand.
to have complete control over someone so that they will do whatever you want
He shrugged off a warning that he is `playing with fire'. Barbara's ex-boyfriendsaid: `She has him in the palm of her hand.'