Laylora, the Paradise Planet, is a world of breath-taking beauty, where peace-loving Aboriginals supposedly live in harmony with their environment. The Doctor and Rose arrive to answer a distress signal from a group of scientists, only to find that the once-perfect eco-system is showing signs of failing.
Pg 35 Laylora, the late 24th century (pg 84).
Pg 34 "'Alarm of some kind' [...] 'Red alert? Mauve?'" The Empty Child.
Pg 38 "Until the main trisilicate engines could be recharged an alternate power source would be needed." Trisilicate featured in The Monster of Peladon. There are a great number of references to it here. I haven't noted them all.
Pg 46 "Rules of Space-Time travel No. 10: don't eat anything until you're sure it's totally safe. Unless it's a badly cooked kronkburger - in which case don't eat it at all." Kronkburgers featured in the comic strip and were mentioned in The Long Game.
Pg 47 Contents of the Doctor's coat include yo yos (the fourth Doctor), a conker (possibly a reference to comic strip Doctor Conkerer) and a cricket ball (the fifth Doctor).
Pg 66 Reference to Mickey (Rose, Aliens of London et al).
Pg 69 "They might not be as weird-looking as the Moxx of Balhoon or the Ood, but these were aliens." The End of the World, The Impossible Planet/The Satan Pit.
Pg 90 "the ship had been found drifting, out of control and out of power, at the edge of Draconian space." Frontier in Space.
Pg 99 "He'd met Cybermen with more sympathy than this woman." The Tenth Planet, et al.
Pg 101 Reference to Mickey.
Pg 108 "It was the look she saw on her mum's face every time the Doctor took her home to the Powell Estate for a visit." We saw the Powell Estate and Jackie in Rose, Aliens of London et al.
Pg 123 Reference to Jackie.
Pg 125 "She remembered her recent visit to ancient Roma and how odd it had been to see whole buildings that in her own time were just piles of old stone." The Stone Rose.
Pg 160 "Not like your Axon or your Zygon, or any other gon come to that..." The Claws of Axos, Terror of the Zygons. But see Continuity Cock-Ups.
Pg 185 Reference to Mickey.
Pg 190 "It's like reading Hamlet before my final edit..." City of Death.
Pgs 205-206 "The Doctor was reminded of trying to run on the shingle beach at Brighton." The Leisure Hive.
Pg 207 "Mickey's gran used to live in an old terraced council house which had a coal cellar." We met an alternate version of Mickey's gran in Rise of the Cybermen/The Age of Steel.
Pg 226 "I once his in a cuboard in 10 Downing Street while the house fell apart around me" World War Three.
Pg 228 ""I promised her mother that I'd look after her" World War Three.
Pg 245 "And she smiled to herself, thinking of her own father. 'You never know, you may have family out there, waiting to meet you.'" Father's Day, Rise of the Cybermen/The Age of Steel.
OLD FRIENDS AND OLD ENEMIES
NEW FRIENDS AND NEW ENEMIES
Rez, Hespell, Baker, Jaelette, Kaylen, Professor Shulough.
Pgs 9/71/105 The Wikitu, hairy bipeds with sharp talons and a dense coat of coarse, dark hair. They're similar to werewolves, with a strong smell of sewat and zoos. In reality, they're villagers who get converted into fearsome creatures whenever the planet gets threatened (pg 153).
Pg 69 Laylorans, aliens who look similar to humans, but who have rounder eyes, flatter noses, pointier ears and hands with only three fingers and a thumb.
Pg 173 A variety of native insects, including midges and butterfly-like creatures.