Germania in the 8th century. Pope Gregory has given Bishop Bonifatius the task of bringing the Christian belief to the heathens of Germania. Bonifatius is on his way to the Duke of the Franks, Karl Martell, with his pupil Sturmius. They ask the Duke for protection and support for their future missionary work and for a place which they can use a centre for their activities. Karl Martell grants them an abandoned royal manor in Buchonia.
Martell also orders his two sons, Karlmann and Pippin, to accompany and protect Bonifatius. Martell hopes that, under the churchman’s guidance, his young sons will mature and become men.
Arriving at the royal manor, they meet Alrun and Luidiger who run a tavern which is the only building which is still standing. Alrun feels strongly attracted to Sturmius and he feels emotions for the pretty girl which are new to him.
The idyllic scene is, however, abruptly interrupted by "The Armies of Odin", which thunder past the tavern. Luidiger tells the guests about these murderous, fire-raising people, who are led by the Fresian Duke, Radbod. Radbod and his followers are on the way to a sacred place where they want to venerate the Donar Oak.
Bonifatius follows the crowd in order to witness this ritual. Acting as a kind of high priest, the heathen Duke, Radbod, praises the tribal god Donar. Radbod’s followers celebrate their gods with song and dance. Bonifatius intervenes and he becomes the target of Radbod’s anger. They start an argument which escalates to a point when Bonifatius grabs an axe and fells the oak with one stroke. By felling the oak he tries to prove to the heathens that their gods do not exist. In awe, the heathens bow to the power of the Christian God.
Bonifatius’ success story seems to be continuing when his cousin, Lioba, arrives from distant England to support his missionary work. Bonifatius baptises the heathens in the nearby river, the river Fulda - the heathens are to renounce their gods. The baptism is disturbed by a mother who accuses the Christian church of enriching itself from the people and oppressing them and, in particular, she refers to Bishop Gewilip of Mainz who has her husband’s life on his conscience. The woman’s husband has worked until exhaustion to able to pay the churchman’s taxes. Bonifatius is shocked. He realises that the heathens are not getting baptised because of their convictions and belief, but rather due to fear and intimidation and he begins to doubt the way he is carrying out his missionary work. He decides to travel to Mainz to form his own opinion of the situation there.
On his arrival in Mainz, Bonifatius meets Bishop Gewilip who is indulging in a decadent life. Gewilip, who has completely turned to worldly matters, is not interested in belief or the Church and totally rejects the strict views of Bonifatius. An argument arises in which Bonifatius threatens the bishop that his decadent lordly life would soon be over and that he would have him deposed by the Pope. Plagued by self-doubt Bonifatius does not sleep the following night and he prays to God to give him the necessary strength to fulfil his difficult tasks and make the right decisions. He gives his student, Sturmius, two despatches which he is to take to Pope Gregory II. One despatch concerns the deposition of Gewilip, the other is a request to establish a self-administering monastery in Buchonia. Accompanied by Karlmann and Pippin, Sturmius sets off on the hard journey to Rome.
When Sturmius arrive in Rome with his two companions, he presents his petitions to the Pope and emphasises the urgency of the matter. Pope Gregory II asks for an exact description of the conditions in Germania and then gives his blessing for the foundation of a monastery and also approves the deposition of Gewilip. As Sturmius is on his way back with Karlmann and Pippin, a conversation between Lioba and Alrun takes place in Buchonia. Lioba explains to Alrun that Sturmius accepted certain obligations when he decided to become a monk. That evening, in a dreamworld, Sturmius and Alrun let their desires run free.
Sturmius and the two brothers return from Rome, stopping in Mainz where they deliver the deposition and excommunication to Gewilip. The deposed bishop falls into a rage and swears revenge.
The three companions come back to Bonifatius and they report to him that the Holy Father has granted the request to found a monastery and removed the bishop from his post. Filled with joy about this good news, they imagine how the monastery will look and the effect it will have on the entire area. The placing of the monastery cross forms the highlight of a happy celebration.
Meanwhile Gewilip is forging an evil plan and turns for help to his former enemy, the heathen Duke Radbod. Gewilip proposes to lure Bonifatius into a trap so that Radbod can kill him. Radbod despises Gewilip, who wants to betray his own people, but he sees the chance to be done with Bonifatius for good so he agrees to the plan.
Soon after, Bonifatius receives a letter from the Pope which contains instructions to continue his missionary work in Dokkum. Fulfilling his duties, Bonifatius departs and takes Luidiger as a companion, while Sturmius is to continue supervising the building of the monastery.
Only a short time later, a messenger brings a written assignment with the papal seal. Bonifatius is to personally describe the conditions in Mainz and the progress of the construction of the cathedral. Everyone present sees that this is a trick. Who could benefit from such foul play? Only a high-ranking churchman could know the papal seal and therefore be able to forge it: Gewilip! Sturmius immediately sets off with his companions and the messenger to catch up with Bonifatius and prevent the worse from happening.
Meanwhile, Bonifatius and Luidger have reached Fresia. The missionary is haunted by a vision of death, but Bonifatius is not afraid as he is sure that his life lies in God’s hands. Suddenly Radbod and his men appear. Luidger tries to protect Bonifatius by stepping in front of him and he is killed in the ensuing fighting. Shocked by Luidger’s death, Bonifatius sees his martyrdom approaching and calls on Radbod to finish his work. Radbod realises the danger that he will render Bonifatius immortal, but his followers urge him to do it and Gewilip, noticing his hesitation, demands that he fulfils his side of the bargain. Finally, Radbod gives into the pressure and stikes Bonifatius down. Gewilip remains alone with the dying missionary and, mocking him, enjoys his moment of apparent triumph.
Sturmius and his followers arrive at the scene too late. When the papal legate wants to arrest Gewilip for treason, the cowardly Gewilip commits suicide. Bonifatius lies dying in Sturmius’ arms and asks his student to continue his work. With a heavy heart Alrun adds weight to this request because Luidger’s and Bonifatius’ deaths should not have been in vain.
Once again, Bonifatius questions the sense of his life. He reaches the conclusion that a person has a particular capacity to believe in himself and the good in man.