I generally like character-driven writing, but sometimes a set-up is so fun, all incidental missteps can be forgiven. "Drop" features a young widow on a first date. She has left her little son in the care of his aunt. The woman, Violet, receives a mysterious message: "Your son is now my hostage. Kill your date--or your son dies. Make any noise about this, and your son dies." Because of the limitations of "drop" technology, Violet knows that the messages are coming from somewhere within a tight circle surrounding her body. Someone in the restaurant is sending the messages. But this is all that Violet knows. Violet is smart and inventive; she tries commandeering the hostess station (where you can send IMs to a domestic-abuse counselor through "support.com"). Violet writes a desperate message on a napkin; she uses lipstick. Moments from imploding, Violet does some fancy work with a lime-slice from a shot of tequila; to say more right here would be...