The Elixir of Doom.

Audio The box art for The Elixir of Doom with its smiling Pertwee and younger version of Jo doesn't quite match the contents since its Eighth who's the Doctor they meet and Jo seems to hark from a time after SJA's The Death of the Doctor (according to the Wikia) which also makes this the only occasion Eighth and Iris meet in something which isn't prose (I think). It's wildly entertaining, a typically whimsical Magrsian tragicomedy about the institial gap between human and unhuman as Iris and Jo investigate why some of the creatures in various 1930s Hollywood features seem more real than they should be.  Stretching the Companion Chronicle format, it feels more like a full blooded audio play with Katy Manning magnificently playing about half a dozen parts including making Jo and Iris such distinct characters that like Tatiana Maslaney in Orphan Black, by the end, you entirely forget they're being played by the same person.  Oh and she gives us her Eighth Doctor who thanks to the script sounds incredibly in character, especially when he and Iris are bantering.  Placement:  Part of the fun of the play is discovering the placement.  Despite Big Finish having previously gone to the trouble of creating a whole new character to account for the mention of Sam Jones during Minuet in Hell, here's Paul Magrs acknowledging her meeting Iris during The Scarlett Empress.  But this also seems to be Jo's first meeting with this incarnation which messes up Paul Leonard's novel Genocide, but since The Death of the Doctor's done that too, time can be rewritten, the cracks, the Faction Paradox, take your pick.  Anyway, the author says it's set during The Scarlett Empress and who am I to disagree?