Mendeb Two was a planet in the Mendeb system.
Mendeb Two and Three were colonised by the TAM Corporation. During a galactic war, they abandoned the system, with a space station and a communication system connecting the two worlds.
The Second Doctor visited Mendeb Two and removed an component of the communications system, unwittingly severing contact between the planets.
Years later, Ace discovered the part in the TARDIS, prompting the Seventh Doctor to return to the system. They found that Duke Vethran had taken over Mendeb Three. The Duke was kidnapping people from Mendeb Two, giving them the mind control drug SS10, then selling them as slaves. Ace eventually gave the drug secretly to Vethran, removing his free will permanently. The Doctor and Ace leave the people of both planets to establish peaceful relations. (PROSE: Independence Day)