The story of the Knights Templar in a somewhat historical manner.
We mostly follow Landry who quite against his own will, becomes the master Templar of the Paris temple when his predecessor dies. The first season is mostly about Landry looking for the Holy Grail that the Templars lost during a lost battle at Akko in 1291. During that battle the grail was lost, but it appears to have resurfaced in France.
Landry is a friend to the King of France (Philip IV 1268-1314), but also the lover the the king’s wife (Joan I of Navarre (1273-1305) which is basically the start of a lot of problems.
In spite of the lost battle of Akko, the Templar Knights thrive under the protection of the Pope and the King of France, but raptures start to appear in the relationship. First, the King of France is after the Grail as well, thinking it would increase his power. To obtain that power, he first sets up the Pope (Boniface III 1230-1303) against the Templar Knights and then even replaces the Pope with Clement V (1264-1314). Both Popes, especially the former, have their own agendas of course.
The series make a drama with love, drama, brotherhood, honour, fighting and battle scenes and a lot of intrigue. Here and there there are historical elements, but do not see the series as a history lesson.
Of course the Templar Knights eventually loose their organisation and their lives, but not without a fight.
Not boring, but not great either.