Roots: Outbreak. Alien abduction stories.
Intertextuality: The first appearance of The Viyrans was in a short story called No One Died from the 2007 Doctor Who Storybook.
Goofs: Peri's sadness and the Doctor's heartache about Erimem doesn't precisely sum up the mood of Bride of Peladon's ending, promising as it seems to a pretty happy ending for Erimem.
Continuity: Grallista Social is a party planet, a resort hosting several species strictly for the purposes of leisure. Partygoers stay in huts and there is a spaceport - the arrival of the TARDIS seems to occur without interest. Grallistan punch rightly deserves its reputation for its potency.
The Viyrans come from an unnamed galaxy which has known only war for millennia. After the end of catastrophic war involving great use of biological weaponry a treaty was signed for the cessation of all agents used, however an accident during the decommissioning released countless variant viruses and biological agents, scattering them across the stars. One such viral sample has entered the atmosphere of Grallista Social and infected Peri, causing her to become patient zero. The Viyrans cannot read minds and have no vocal language - they assimilate Peri's language to communicate with her. They attempt to wipe Peri's memories, failing 338 times to achieve "Memory Zero". Peri is familiar with the concept of patient zero.
Virus 7001 copies the host DNA and is transmitted aerobically. It attempts to mutate the DNA of the victim into that of patient zero. The subsequent genetic mutation is crude and destructive, killing each of its victims slowly and painfully.
Links: Peri's memories reference The Mind's Eye (her imaginary son Kyle), Son of the Dragon (Dracula) and, obliquely, Bride of Peladon (Erimem's departure). The nature of virus 7001 and the Viyrans' 'glass coffins' is explained further in Patient Zero, which also features a brief return to Grallista Social.
Location: Grallista Social
The Bottom Line: "Memory zero, negative. Reset."
Surreal and disorientating. The slightly skew throwaway lines about Erimem (see above) aside, Mission of the Viyrans is an immediate standout for its disconnection from any of its neighbours - that and the ambiguous ending, all of which beg for further detail. When that finally arrives in later stories 'Mission' pays dividends.
THE VIYRAN STRAND
Big Finish's 'Virus Strand' mini-arc, comprising (in chronological order) Urban Myths, Mission of the Viyrans, Urgent Calls, The Wishing Beast and The Vanity Box is a loose collection of short stories (Wishing Beast aside) each involving a 'viral' aspect in the obstacle met by the Doctor and his companions (again, Wishing Beast is different as it shares the same viral creature with its immediate sequel The Vanity Box). The arc is further explored in Patient Zero (where the nature of the Viyrans is explained) and ultimately Blue Forgotten Planet - although elements of the arc (specifically Dalek involvement in the station) also reappear as a back story for To the Death. For each story the virus is wildly varied and not always easily identified, representing a different strain or viral agent and usefully indicating the enormity of the task the Viyrans have been set in retrieving and destroying them. Indeed, it's conceivable that the origins of these viruses in the distant past could allow for other viral entities in the wider series - the Virus of the Purpose from The Invisible Enemy, for example, being included among those sought after by the Viyrans; however this is an idea not explicitly encouraged by the creators of the arc.