O is for... Ogri

Silicon-based creatures which are native to the planet Ogros. In appearance they resemble large misshapen stone blocks, which glow from within when active. They have the power to move, and feed on certain amino acids in their native, swampy habitat. These same chemicals are to be found in blood, and they hunt and kill mammalian life – including humans - for sustenance.

The criminal Cessair of Diplos removed a number of them from Ogros to utilise as weapons, and they were being transported with her on a prison ship which became stranded in hyperspace. She escaped to prehistoric Earth – arriving in the remote western region of England. The stones were hidden in a neolithic stone circle which came to be known as the Nine Maidens. This circle attained the reputation of being impossible to count - the number changing each time. This was due to the occasional movement of the Ogri.

Cessair set herself up as an authority figure in the district over several centuries, changing her identity to prevent detection.

When the Doctor and Romana arrived in search of the third segment of the Key to Time, she was posing as a woman named Vivien Fay, who had befriended archaeologist Professor Emelia Rumford, who was conducting a survey of the Nine Maidens.

Fay posed as a Celtic deity known as the Cailleach, whose worshippers offered blood sacrifices to the Ogri, unaware of their alien nature.

She used the creatures to dispose of the coven when the Doctor and Romana began to investigate. K-9 was badly damaged when it attempted to defend the Doctor and Rumford from an attack by an Ogri. Once repaired, K-9 could at best hold them at bay with its nose blaster.

One Ogri was destroyed when the Doctor lured it over a cliff and into the sea, whilst another was reduced to rubble by the Megara – justice machines which had been escorting Cessair on the prison ship.

The remainder were captured to be transported back to Ogros, whilst Cessair was transformed into a new standing stone by the Megara.

Appearances: The Stones of Blood (1978)

• It was originally intended that the Ogri would be realised as a man-in-a-suit costume, but VFX designer Mat Irvine insisted that they be props.
• The scene in which an Ogri attacks a pair of campers was added due the episode under-running.