The Missy Chronicles, by James Goss, Cavan Scott, Paul Magrs, Peter Anghelides, Jacqueline Rayner and Richard Dinnick
Second para of third story ("Teddy Sparkles Must Die", by Paul Magrs):
Jack spared his younger sister a scornful glance. ‘I’m not scared of her. She’s only a servant.’Six stories here, and reading through other people's reviews I am struck by how different everyone's take is. However, most people single out "Girl Power!" by Jacqueline Rayner as a favourite, and I agree - it's set during Missy's years of imprisonment in the Vault, in the style of internet chat between her and famous women of history as she tries to develop a cunning plan for escape and domination but ends up getting changed herself.
The opening story, "Dismemberment" by James Goss, was a (very) rare miss for me from this writer; I simply found it too violent. However I go against fannish consensus in rather enjoying "The Liar, the Glitch and the War Zone" by Peter Anghelides, which features the first appearance of the Thirteenth Doctor in written fiction. I am more with the mainstream in having enjoyed Richard Dinnick's "Alit in Underland", set between the TV episodes "World Enough and Time" and "The Doctor Falls", and exploring what Missy and the John Simm Master got up to on the Mondasian colony ship. Well worth getting.
The Legends of River Song, by Jenny T. Colgan, Jacqueline Rayner, Steve Lyons, Guy Adams and Andrew Lane
Second para of third story ("A Gamble With Time", by Steve Lyons):
That's on Earth, in case I haven't mentioned it before.Again I think Jacqueline Rayner has the best story here, "Suspicious Minds" featuring an Auton version of Elvis and a bunch of hints at River's own past. I also liked Jenny Colgan's "Picnic at Asgard", which fills in that particular gap in continuity, and "River of Time" by Andrew Lane which actually has River functioning as an archaeologist.
I think this collection works better than The Missy Chronicles, basically because River Song is a more interesting and more complex character. You can get it here.