In February 1836, Texas is part of Mexico, and most of the English and Spanish speaking settlers of that region are discontent with the tyrannical rule of Gen. Santa Anna. General Sam Houston (Richard Boone) arrives in a small town with several men where he hastens to assemble a Texan army. At the same time, Santa Anna is heading north with several thousand soldiers to defeat the rebellion. To gain more time, Houston orders Col. William Barret Travis (Laurence Harvey) to take command of the Alamo, a fort in a crumbling mission near the village of San Antonio de Bexar, through which Santa Anna's men must pass. Houston hopes that Travis and his 27 "regular" army men will stall the enemy for as long as possible with the assistance of rancher Col. James Bowie (Richard Widmark) and his 100 Texas volunteers. The hard-drinking and independent Bowie, who has extensive landholdings to protect, and the aristocratic and arrogant Travis are a poorly matched team and antagonism between the two officers quickly grows.Although Juan Seguin (Joseph Calleia), a respected community leader, reports that Santa Anna is closer than they realize, Travis refutes the information and repeatedly lies to the men about the danger of their situation. Believing that most men have no capacity to act for reasons of honor, Travis tells his confidant, Capt. Almeron Dickinson (Ken Curtis), that the men would desert their posts if they knew the truth.Meanwhile, Colonel David Crockett (John Wayne), a former U.S. Senator, and his rowdy, but loyal 32-strong Tennessee backwoods sharpshooters, arrive in Bexar and head straight for the cantina. Travis seeks out "Davy", and is surprised to learn that the reputed "illiterate country bumpkin" is an eloquent, deep thinker and is sensitive to the Texans' plight. Aware that Santa Anna's regime forbids Texans economic rights, Davy has also guessed the unpublicized plans to create a Republic of Texas. Unknown to his men, who think they are out for adventure, Davy has brought them to Bexar to investigate the situation and possibly convince them to join the fight.Crockett soon falls in love with Flaca (Linda Cristal), a young Mexican woman whose family was killed by Santa Anna and who is being pressured to marry Emil Sande (Wesley Lau), a local merchant who has curried favor with the Mexican general. Although she refuses Davy Crockett's gallant offer of help, she tells him about the cache of ammunition Emil has hidden for Santa Anna in the basement of the village church. During the night Crockett, Bowie and their men find the supplies. When Emil discovers Davy and the others and tries to kill them, Davy throws Bowie's knife at Emil, killing him.Crockett and Flaca enjoy a brief romance, but he soon sends her north to safety, realizing they may never see each other again. Travis keeps up the morale in the fort by reporting that Captain Jim Fannin is on his way to the Alamo with more soldiers. Believing that staying cornered inside the fort is suicide, Bowie unsuccessfully tries to convince both Travis and, later, Davy that the best way to defend the Alamo is by a "cut, slash and run" approach out in the open. Davy Crockett convinces his men to fight for the Alamo by reading them a letter, purportedly