Roots: Asimov's Laws of Robotics. The Doctor mentions Stockholm Syndrome.
Dialogue Triumphs: 'One death is more than enough to have on your conscience. So why not take on all those deaths on myself, save anybody else from having to take them on?"
Continuity: Consensus space is a backwater system with one sun and nine planets, two of which are populated by a total of two billion people. Travel is by shuttle. There is mention of a 'Staynis' colony where people have died in its deserts. This area of space was subject to feudal infighting for decades, costing millions of lives until the intervention of a self-appointed leadership, Consensus. In time this authority itself became corrupt and protective of its power, using the threat of the system's sun's collapse as a deterrent against rebellion. Upon his arrival the Doctor joined the rebellion but was captured and forced by Consensus to work on the planet on the former monitoring station.
The substance of the Mercurials behaves and looks a lot like mercury, and can withstand great heat, so the race is often found on the hottest planets of various systems. They can be vulnerable to powerful gravitational forces. They are mercenaries, hiring themselves out to whomever pays, often for unpleasant or unsafe jobs. Mercurials are vulnerable to multiple simultaneous frequencies which undermine their physical integration.
Daphne the android is self-repairing. Androids have no tastes sensors. Previous models accompanying the Doctor were named Annie, Bethany and Chloe. The core programming of an android disallows the model to work against their maker.
The Doctor arrived alone and is in the prison for six years, his prison being a hexagonal looped corridor with a DNA-coded force field. The cover story for the resistance is that the Doctor is dead, "the greatest martyr of his age." The Doctor wears pyjamas. He has a voice program called LM-voice for his androids.
Location: Consensus space, time unknown.
The Bottom Line: "This isn't a prison of walls. It's a prison of responsibility"
Taken alone, a typical Robson run-around with mad technology and stupid humans, as a break between bigger arcs it's less satisfactory, and feels less like a break for the inclusion of Sheridan Smith's voice (even if it is nicely written in there). As a de facto companion, not-Lucie can't help but some across as a bit of a misstep, sorry.