The story of Guy Aylmer, a young 17 year old esquire and man-at-arms, whose leige lord, Sir Eustace, is a knight with castles and allegiances in both England and France during the Hundred Years' War. Guy's father is castelain over Sir Eustace's lands in England when Sir Eustace is away in France. Guy is second-in-command over a contingent of 30 men-at-arms and 25 English longbowmen serving in defense of Sir Eustace's castle in France during the disturbances following the Duke of Burguny's murder of the Duke of Orleans, the brother of the sometimes-mad King Charles II of France.
Some of the Orleanists take advantage of Henry IV of England's prolonged inactivity, by attempting to storm Sir Eustace's castle in the absence of an English field army. Thanks to the English archers and men-at-arms, Sir Eustace repels the attack, infflicting heavy losses on the Orleanist raiders.
Despite this evidence of his determination to hold his castle in Villeroy for King Charles, Sir Eustace worries that the Duke of Burgundy will now become a threat, and so it turns out when he receives a command in the King's name (clearly under Burgundy's influence) to either admit a French garrison or send his wife and children to Paris as hostage for his fealty to King Charles II. Sir Eustace's wife, Dame Margaret, decides to accede to the "King's demand" and rides to Paris with her 14 year old daughter Agnes, her nine year old son Charles, and young esquire Guy in command of her escort consisting of Long Tom the archer, and three of Sir Eustace's French men-at-arms.
In Paris they find that their lives are threatened by the market guilds headed by the Butchers' Guild, who are virtually a law unto themselves. In fact, within days of their arrival, their residence is attacked by hundreds of armed Butchers chanting, "Death to the English Spies!" despite Dame Margaret's status as a hostage under the King's nominal protection. The Butchers are really out to murder their host, the head of the Silversmith's Guild, and then lay their hands on his store of silver treasure.
Thanks to a timely warning from a dispossessed Italian Count with a taste for intrigue (and using astrology to foretell the future), Guy and Tom and the three men-at-arms barricade the doors and the staircase and hold out until some Burgundian knights, one of whom Guy and Tom had rescued from a mob, arrive to disperse the Butchers, in response to a message carried by the Count's daughter, Katarina, who was accustomed to carry messages for her father while being disguised as a boy. The knights find dozens of bodies littering the doorway and stairs, most killed by Long Tom's arrows, and express their approval of Guy's clearheadedness and bravery, and of Tom's skill as an archer.
Later Guy recieves word that the market guilds intend to demand that Dame Margaret and her party, as well as the French knights who came to their aid, be handed over to face trail by a guild tribunal for the deaths they caused. Guy sends a warning to the French knights, telling them to flee the city, while Dame Margaret and her children hide with the Italian Count, who is accustomed to concealing many aspects of his vocation and daily life, and hopes to send his daughter Katarina to England to reside with Dame Margaret when the danger in France becomes too great for her to remain.
Guy, Long Tom, and the French men-at-arms assume disguises to remain close by. Numerous other arrests and executions are made by the guilds, most of their victims being of the Orleans faction, and Guy has to rescue Katarina from a group of Butchers.
Then when the Orleanist forces seem about to assert control in Paris, Dame Margaret makes plans to escape and return to the castle at Villeroy under the protection and escort of their friends, the Burgundian knights. Eventually the Count brings Katarina to join them and they leave for England where the new king, Henry V is preparing to invade France in response to broken French agreements, and to retake lands which had been lost during King Henry IV's reign.
The king has heard the story of Guy's adventures in Paris and asks Sir Eustace to assign Guy to be near him if they are forced to fight, so that he can witness Guy in action, and reward him properly. So it happens that Guy is on hand on October 15th, 1415,at the Battle of Agincourt and is able to rescue the king himself when Henry is temporarily stunned by a blow from a French battleaxe.
This is the occassion for one of the Count's astrological predictions to come true, namely that Guy would eventually become a knight "at the hands of a king," which entitles Guy to wear a suit of armor that had been given to him by the grateful silversmith. Later Guy wins promotion following a sea battle to knight coronette with a castle of his own , together with two adjacent manors. Guy and Katarina are betrothed, and King Henry V attends their wedding, and takes the first dance with the bride himself.
And thus the Count's other prediction was fullfilled, that Guy would win not only his kinght's spurs, but an estate of his own,... and that he would marry an heiress.