MEXICAN HEAT… For Annie McCallister, divorce was just another item for her list of failures. But here in Puerto Madero, she'd found a haven...good friends...time to forget...and the children. Her little refugees. She'd handled their tears, fears, spats and hurts with remarkable aplomb. She loved them - and they loved her. Then she met the dark, passionate Luis Calderone and felt a yearning excitement she'd never known. She wove a spell around him that he both relished and resented. Anna - his beloved gringa - a strange, funny woman who'd come into his well-ordered life trailing a confusion of children behind her - and making him smile.