The Disorderly Knights1966
by Dunnett, Dorothy.
Back in Scotland, Crawford establishes a trained force of mercenaries and encounters Joleta Malett, a beautiful and wilful teenager. Through her brother, Graham Reid Malett, a knight of St John of Jerusalem, (who will also be a central figure in the next book of the series, Pawn in Frankincense), Crawford is enticed to Malta to help the Order's defence against the Turkish forces of Suleiman. This section of the book (the defence of Mdina, Gozo and Malta in 1551) closely follows historical events. Back in Scotland, and accused by his brother and companions of debauching the lovely Joleta, Crawford's rivalry with Malett results in the death of some of the series' most attractive characters, and culminates in a dramatic showdown between the two in Edinburgh.
This is an historical romance...