What makes a story intriguing? A look at two kidnapping stories

A character does something big and bold--something out of the ordinary and maybe out of character, surprising other characters, and even themselves. 

In the British TV series Upstairs, Downstairs, Mrs Bridges the cook steals a baby from its pram outside a shop and hides it in her room. What was her state of mind? Guilt-ridden over the suicide of her young kitchen maid Emily the week before, Mrs Bridges now sees "the poor thing" she had criticized relentlessly as the daughter she never had. The baby-snatching shocks all who know their cook as a stable member of the household. Viewers, too, have got to know her by this time (episode 9 of season 1, "Why Is Her Door Locked?").

In the opening scene of Not Her Daughtera new novel by Rea Frey, a young woman is running down a road in the rain gripping the hand of a five-year-old girl. Told in first person present, she is in the throes of the act of kidnapping. All we know about the three main characters is on the book jacket: the kidnapper is an entrepreneur and had her first encounter with the child and its mother in an airport. And, in capital letters, the book is soon to be a major motion picture. Like TV commercials that tell stories in a minute or less, the novelist and publisher ask readers to identify with the characters by type (single childless women, mothers) and call upon their own experience in airports and crowds.

Which kidnapping story do you find more intriguing? The Upstairs, Downstairs episode was made in 1972 and features a secondary character, an elderly cook beloved by viewers who have come to know her.  But Not Her Daughter, a standalone novel, features characters of the same age, socio-economic background and race of its targeted readers. Will all women of the same type as the kidnapper and mother find the opening intriguing? 

How much do we need to know about a character for a story to catch us in its grip? Is type enough or do we need characters with substance? Will an exciting action scene capture and hold our attention, or do we need to see characters as unique individuals like ourselves in stories that surprise us?