warning: possible spoilers.
This is a remake of the 70's "Pelham 123" movie; Denzel plays Walter Garber, a dispatcher in the subway control center. He notices unusual activity by the Pelham 123 subway train and soon gets the call from a hijacker/kidnapper named Ryder (Travolta), who has hijacked the train and is holding the passengers hostage. He demands $10 million for their safe release. The mayor (James Gandolfini) is brought in to oversee the negotiations and ultimately approve the payment. It is later revealed that Ryder never intended to release them. They later find out that that the hostage situation is affecting the stock market and commodities, specifically gold, and this was all part of the plan.
The story is interesting and well-told. There is also plenty of action. As you'd expect, Denzel Washington and John Travolta were both very good; I particularly enjoyed the interaction of their characters. Ryder does seem to take a liking to Garber, and will only negotiate with him, but he ultimately gets Garber to confess something he did which turns out to be an integral part of the story. Ryder is a former Catholic.
Content Warnings: Mainly language. It seemed like every other scene had the 'F word'. There was no reason for this; it would have been a better movie without it.
Violence, especially one particularly bloody gunfight toward the end. NOT FOR KIDS.