The year is 2013 and on a day in April all citizens of Boston USA are excited due to the marathon being run. Almost the entire population of the city is either witnessing or taking part in the marathon. A large number of policemen have been employed. Suddenly a huge explosion rips through the crowd killing and injuring many. In the ensuing chaos and confusion policemen try their best to evacuate people and arrange to have the injured sent to hospitals. The law enforcement agencies now get together to investigate and catch the culprits. The team consists of Kevin Bacon, special FBI agent ; Mark Walberg, police Sgt ; JK Simmons, police Sgt and some others. The local Police commissioner and Mayor along with the Governor of the state are active in the investigation. With the help of modern technology of surveillance and forensics they are able to pinpoint the culprits.The culprits are located and a fierce gunbattle follows where one of the culprits dies. The other one is soon caught hiding in a boat of an alert citizen.All this takes about 5 days of painstaking investigation. Director Peter Berg recreates the entire incident admirably and presents an edge of the seat suspense thriller. There are also a good number of emotional scenes which convey the mood of the people at that time. It is a case of community courage in adverse conditions and about the strength and resilience of the human spirit. Actors Mark Walberg, Kevin Bacon and JK Simmons have particularly turned in superlative performances.