Merlin Investigation Series by J.M.C. Blair

Merlin makes a great investigator—and it only looks like magic.Merlin is no magician, merely a scholar and advisor to King Arthur. But after the supposedly magical Stone of Bran is stolen along with the legendary sword Excalibur and one of Arthur's squires is brutally murdered during the theft, Merlin must use the power of reason to conjure up a miracle and catch a murderer.

When Lancelot is accused of murdering Queen Guenevere's father, she begs Merlin to prove his innocence. Though inclined to leave the faithless knight to his fate, Merlin risks his very life to find the truth at King Arthur's bidding.

Merlin investigates a royal mystery at Stonehenge. A baron and his sons are found dead at Stonehenge. King Arthur's potential heirs start to mysteriously die. And only Merlin can prove that the murders are not the work of the plague, but something much more sinister.