Spoilers: ENT "Shockwave I and II", "Storm Front I and II"
DW: "The Doctor's Daughter" and the movie "The Five Doctors"
Other Notes: The Death Zone was an area of Gallifrey where the Time Lords used people in 'The Game'. The object of The Game was to find the Tomb of Rassilon (or the Tower of Rassilon) and escape the Death Zone safely. There were mountains, marshes, thick mists, and complicated traps that made the Game deadly.
The Companions traveled with the Doctor in his various incarnations. The ones listed in this chapter are Martha Jones (Ten), Donna Noble (Ten), Jenny (the Tenth Doc's daughter, but not a real companion), Romana I and II (Four), Sarah Jane Smith (Three and Four), K-9 Mark II (Sarah Jane's "pet", Four), Jo Grant (Three), Grace Holloway (Eight) Amy Pond (Eleven), Rory Williams (Eleven), River Song (Future Companion (?))
Note: There's one important Companion missing from this list. Who is it?
Ianto Jones, Owen Harper, Gwen Cooper and Toshiko Sato were the other members of Jack Harkness's Torchwood. Martha worked with them for a time.
( Interlude in Infinity 3: The Death Zone )