Michael Cronin

When his weekend hostess is found murdered, Hastings sends for his friend Hercule Poirot.

As Bayard and the Knights of the Western Isles are welcomed to Camelot for a feast, Nimueh infiltrates Bayard's entourage and begins a plot to get revenge on Merlin. Posing as a servant girl, Nimueh tricks Merlin into drinking from a poisoned chalice. Falling gravely ill, the only chance Merlin has is for an antidote to be prepared. Arthur takes it upon himself to retrieve the needed ingredients but, with Nimueh doing everything she can to thwart Arthur's quest, will they be able to save Merlin in time? Bayard and the knights of the Western Isles are welcomed to Camelot for a feast celebrating a union between the two kingdoms. Nimueh, however, has other plans. Posing as a serving girl, she infiltrates Bayard's party and enters Camelot with a view to seeking revenge on Merlin. Unaware of her true identity, Merlin befriends the young serving girl. Once she has gained his trust, Nimueh warns him that Bayard isn't the friend he seems as he plans to poison Arthur. Merlin bursts into the banquet and stops Arthur drinking from a poisonous goblet in the nick of time. Bayard denies trying to poison Arthur and Uther decides that the only way to determine the truth is for Merlin to drink from the cup himself. Merlin falls to the ground, poisoned. The guards arrest Bayard and his knights. Merlin falls into a deep coma. Gaius discovers that Merlin has been poisoned by the Morteaus Flower and can only be saved from certain death by an antidote made from the leaf of the same plant. However, the flower is rare and only grows in the caves of Mount Argeaus, which are found deep within the forest of Balor. As Merlin's health deteriorates fast, Arthur, humbled by his servant's bravery, believes he must set off on a quest to retrieve the flower himself. But Uther forbids him to go because the danger is too great. Morgana counsels Arthur and helps him realise that he is his own man and should do what he thinks is right, even if it means disobeying Uther. Will Arthur find the flower in time to save his friend or will Nimueh place more danger in his path?

A new physician arrives in Camelot and stands to threaten more than just Gaius's job. A mysterious and scarred man enchants a bunch of flowers which are then delivered anonymously to Morgana. As she sleeps, an enchanted beetle creeps from the bouquet and enters her ear, making Morgana seriously ill. Gaius is summoned to help but, unaware that it is magical, cannot find the cause of the disease. Edwin, the scarred man, arrives at the palace – he is a physician and claims to have a cure for all ills. Desperate for answers, Uther urges him to start examining Morgana right away. Edwin secretly uses magic to remove the beetle from Morgana's head, thus curing her of the illness. Though grateful for his help, Gaius is suspicious of the mysterious stranger and his methods. Uther, meanwhile, is impressed and encourages Edwin to stay on in Camelot. Merlin is curious about Edwin and takes it upon himself to see what he can find out about this mysterious stranger. Snooping around the physician's chambers he finds a wooden box of "dead" beetles. Reading the spell on the lid, Merlin accidentally conjures the beetles to life. Edwin catches Merlin and realises he must have magical powers to be able to perform such a feat. Meanwhile, Gaius starts his own investigation, and enlists the help of his old friend, Geoffrey of Monmouth. Gaius manages to get his hands on a copy of an old records book from the time of the Great Purge. Studying the book from dusk till dawn, Gaius finds what he was looking for – evidence of Edwin's true identity. Deeply concerned for the King's safety, Gaius visits the Great Dragon looking for advice, but doesn't like what he hears and leaves Camelot. Merlin is devastated.

A mysterious knight arrives in Camelot, uncovering a secret from the past that Uther would prefer stayed buried. At Arthur's coming-of-age ceremony, the celebrations are interrupted when a mysterious Black Knight crashes his horse through the window. He throws down his gauntlet and challenges the knights of Camelot to single combat. Sir Owain, a young, eager knight, picks it up and accepts the challenge – they will fight the next day. Uther is as white as a sheet as he watches the knight go, staring intently at the distinctive crest which marks his helmet. The following day, a large and nervous crowd gathers to watch the fight. Sir Owain strides out to the waiting Black Knight and the pair do battle. The Black Knight is an awesome warrior, and it looks like Sir Owain doesn't stand a chance. However, Merlin is delighted when the young knight successfully strikes his opponent. He sees the blade go in but the Black Knight doesn't even flinch and, seemingly unaffected by the blow, he goes on to slay Sir Owain. Later, Gaius takes Merlin down into the crypt below Camelot and to the tomb of Tristan De Bois. Gaius is horrified to see that it is empty – his body has gone. Merlin listens as Gaius explains that the mysterious knight bears the crest of Tristan De Bois, who was the brother of Uther's wife. Driven mad with grief, he blamed Uther for his sister's death in childbirth. Gaius tells Merlin that he thinks the Black Knight is Tristan De Bois, brought back from the dead to exact his revenge. Merlin discovers that there is only one way to kill a vengeance wraith – with a sword forged in a dragon's breath. But is it too late for Arthur who, determined not to lose any more of his knights, is due to fight the Black Knight the following day?

The first episode of this exciting two parter sees Uther captivated by his latest guest, the beautiful Lady Catrina (Sarah Parish). Arthur is appalled by his father’s flirting but Merlin’s wary for a different reason – he suspects she is really a troll! Catrina and her strange servant Jonas (Adam Godley) are welcomed into the heart of Camelot and it is up to Merlin to prove she’s a monster and save Uther from ruin. Unfortunately, Catrina has her sights set on a far greater prize than the King’s heart. Can Merlin overcome her powerful troll magic before it’s too late?