The Crystal of St Helena is the seventh episode of Series 5.
Previous Episode: The Patient
Next Episode: The Wasp
Stark receives some intel from an informer called Madame Elvira warning him that The Grand Master has built a super weapon with only one missing component - a long lost treasure called the Crystal of St Helena, which is believed to made of pure tritemorite. Madame Elvira tells Stark that The Grand Master has a team looking out for the crystal and is close to discovering its location. What Stark doesn't know is that Madame Elvira is actually The Grand Master in disguise.
Panicking, Stark assigns the team to track down the crystal before The Grand Master and prevent him completing the weapon. To help them, he brings in Vinnie, a teenage archaeologist and leading expert on the crystal. Rose and Vinnie share a love of archaeology and immediately warm to each other. The first clue is an ancient diary exhibited in the National Museum, where the St Hopes students are going on a school trip. As the class are led on a boring tour, Vinnie manages to distract them for long enough for Oscar to scan the diary and find a clue that leads the team to a portrait in another section of the museum. A scan of the portrait reveals a picture of a nearby monument, so the team and Vinnie leave the museum to follow the trail.
Oscar and Carrie start to become frustrated by Vinnie's dismissal of their help and wonder why he's so impatient to reach the crystal - perhaps Vinnie isn't all that he seems. The team discover an underground chamber by the monument and head inside. The Grand Master sends a message to M.I.9, informing them that he will use his super weapon to vaporize Big Ben that evening. As a worried Stark and Frank read the message, another alert flashes up onscreen to say that someone has been impersonating Madame Elvira.