Plot = unfolding events in your story:
"Once there were three princesses whose father, the king died." Then the Queen died."
Premise = underlying idea that supports plot and is specific to the motivations/actions of your characters in reaction to the conflict:
"Once, a very old King looked into the eyes of a swan and fell in love. The swan was a young woman under a curse. The King and the young woman were married beneath a full moon, despite his being quite old and her having the form of a bird by day. Shortly thereafter they had three daughters. Then the King died and his wife woman fell into deep irreversible sorrow. She almost died of a broken heart, but chose to live to watch her daughters grow up. Then she died."
Theme = the purest sense of what you are trying to say with your story:
"Without true love, life is not worth living, unless you have daughters." :-)