Six months have passed since Susan Mendes successfully implemented a shift system in the Dalek mines on Vega 6, giving the human slaves periods of rest and food, and giving them enough hope to go on living under Dalek rule. But although she knows she did what she had to to survive, she hated herself for giving in to the Daleks’ demands. When the Dalek Supreme in Seriphia ordered her to travel about the galaxy, bringing hope to the other Dalek-occupied worlds so their slaves would work at peak efficiency, she agreed to do so, but only on the condition that her friend Kalendorf be allowed to travel with her. She claimed to need him by her side in order to give her hope to go on... and thus they’ve travelled from world to world, spreading a message of hope under Dalek rule, while Kalendorf has been spreading a telepathic message of his own. But Kalendorf isn’t happy with the changes he’s seen in Suz, who actually seems to be proud of what she’s “accomplished”. Finally, one day in the Garazone central bazaar, he calls her on it, pointing out that she’s the only one of the Daleks’ slaves who volunteered for her position. These words hurt her, as only the truth can.
Suz and Kalendorf are aware that the Daleks are watching them, but are unaware of the extent of the Daleks’ surveillance. A complete record of Suz’s behaviour is being transmitted back to Seriphia, where the Dalek Supreme and Emperor are analysing it for their own purposes. Suz has become known as the Angel of Mercy, and her work has saved the lives of millions, but the Dalek Emperor is aware that the moral complexity of her situation may compel her to act against the Daleks somehow; such is the nature of the Human Factor. But for now she must be kept alive; she will be exterminated only on the Dalek Emperor’s say-so, and not before...
Suz storms off after her argument with Kalendorf, and thus isn’t there when the slave leader Wernay contacts Kalendorf with bad news. The slaves on Garazone moon K-5000 are refusing to work; a young hothead, Morebi, has heard Kalendorf’s telepathic message urging people to wait and plan for a rebellion, but he’s acted far too soon. Morebi has something to prove; when the Daleks first invaded, Morebi’s entire family was slaughtered, but he surrendered to save his own life and has never forgiven himself for it. Kalendorf goes alone with Wernay to K-5000 to talk sense into Morebi, but they arrive too late; the rebellion has begun, and the corpses of Robomen lie scattered about the moon as the rebels torture their Dalek supervisor in a burning warehouse. Kalendorf is furious; it took half of Morebi’s “army” to destroy one Dalek, and when its casing was blown apart it sent an automatic distress signal to the Daleks on Garazone Central. Reinforcements will already be on their way.
As far as Kalendorf’s concerned, Morebi and his people have thrown away their lives and risked the entire rebellion on a pointless, empty gesture; they must bide their time, and lull the Daleks’ suspicions, until they are ready to act. Kalendorf’s people, the Knights of Velyshaa, lost a war with the people of Earth long ago, and Kalendorf’s spent his entire life under the yoke of conquerers, training to fight a war which may not even be fought in his own lifetime. If he can do it, why not Morebi? But now the Daleks know that something’s up, and they’ve come to K-5000 in force, bringing Suz with them. If the Daleks suspect even for a moment that the Angel of Mercy has been doing anything but convincing their slaves to work peacefully, then all of their work so far will have been for nothing.
Suz manages to convince the Daleks that Kalendorf must have come here to talk the rebels into surrendering, and they reluctantly allow her to try the same. But Morebi no longer cares about mere survival, and vague promises of an eventual rebellion are no longer enough to pacify him. Suz thus returns to the Daleks... and tells them that Wernay has incited a rebellion against their authority. The Daleks exterminate the horrified Wernay and slaughter the rebels without mercy. Replacement slaves are shipped in from Garazone; the K-5000 mines will be working back to full capacity within a day. Kalendorf is appalled by what Suz has done, and by what she’s becoming, but she insists that she had no choice; if the rebels had in fact surrendered, the Daleks would have interrogated them and learned that Suz and Kalendorf have been organising a rebellion against them. She had to do what she did, for the greater good. Didn’t she?
Human ships don’t travel as quickly as the Dalek saucers, and Alby Brook and Gordon Pellan have thus spent the last six months in hypersleep, travelling from the Vega system to the Garazone sector. Oddly, Pellan has woken up first, and Alby finds him using his training from the Vega News ship to intercept and decode Dalek transmissions. It appears that the Daleks are moving Suz again -- and Alby is quite surprised to learn that Kalendorf is with her. This time she’s being sent to Guria, which is close enough to Garazone for Alby to catch up with her this time. As their Drudger pilot sets the ship’s course, Pellan brings Alby up to date on the past six months; the Dalek advance has continued, and Guria is on the edge of their territory in this galaxy. Alby’s only concern is for Suz, although even he admits that he doesn’t know what he’s going to do when he finds her.
Guria is a windswept ocean world, and this is the bad season; the stability of the drilling platforms is at risk, and oil production is thirty percent below the Daleks’ projected quotas. The commander of the Dalek forces on Guria summons the Gurian Highness and his Daughter, and orders them to make their people work harder. Highness and his Daughter simply laugh, and tell them that their biosphere has an angry temper and that their people are sick at heart. They’re aware that the Daleks have little understanding of metaphor and find laughter disagreeable; they’re just trying to irritate the Daleks without ending up dead, while learning more about the so-called Angel of Mercy. They’re surprised to learn that the rumours are true; she does exist, and the Daleks are sending her to Guria.
Alby and Pellan have arrived, apparently without being noticed -- or so they think until they stumble across a lone Dalek on patrol in a trans-solar disc. The Dalek orders them to identify themselves, and Alby, desperate, tells Pellan to send one of the call signs which the Vega News codebreakers picked up. This seems to do the trick, but Pellan’s triumph is short-lived; when the patrol Dalek reports back, the Gurian forces recognise the call sign as that of a patrol from Vega, realise that there are no ships due in from that sector, and soon determine that the ship in question is an Earth Alliance scout vessel. Just as Pellan and Alby think they’re in the clear, they come under attack from an entire squadron of Daleks on trans-solar discs -- but just as the commander is about to give the command to destroy them, it receives an important message from Seriphia. As Alby and Pellan descend into Guria’s atmosphere, Pellan picks up an encoded message, apparently from the Gurian rebels, giving them safe co-ordinates for a landing site. Alby promptly changes course, and the pursuing Daleks are destroyed by covering fire, giving Alby and Pellan the opportunity they need to land.
As Suz and Kalendorf approach Guria, they notice the Daleks preparing for a battle, and the saucer begins to slow down earlier than they’d expected. Kalendorf finds it interesting when Suz wonders if something wrong; if things are going poorly for the Daleks, doesn’t that mean that something must be going right? She’s really starting to think like a Dalek herself... By this point Suz would almost welcome being blown to bits by a well-meaning Earth cruiser, but Kalendorf knows that she won’t get off that easily. The Daleks seem to be preparing for a major engagement, and when Suz and Kalendorf are sent to the command deck they see that Earth Alliance forces are making an unexpected advance into the Guria system. The Earth forces are superior in number and firepower, and according to the Dalek Supreme, Suz’s life is of more importance than winning this engagement. The Daleks thus hold back, but for some reason they force Suz and Kalendorf to remain on the command deck and watch as the Earth Alliance forces launch their attack on Guria. Kalendorf’s happy enough to watch Daleks being slaughtered, but Suz is puzzled; what can the Dalek Supreme gain by making her watch their defeat?
Alby and Pellan have crashed in the sea; their ship is barely afloat, and the Drudger expires after opening the viewports. Fortunately, the ship drifts to land, and they manage to get out moments before it smashes up against the rocks and sinks. Alby forces Pellan to climb up to a nearby cave for shelter, but Pellan has had enough; his hands are going numb from the cold, and he doesn’t know why he’s risking his life for the sake of Alby’s love life. In fact, he isn’t convinced that love really is behind all of this; while he was working with Vega News, before the Dalek invasion, he’d heard rumours that Suz’s employers, the Rhinesberg Corporation, had a top-secret contract with the Earth Alliance Space Security service, something called “Project Infinity”. Alby claims that he’s never heard of it, which is ironic, since, as he now admits to Pellan, he’s a security agent himself. He came from a broken home in the slums of Proxima Major, and joined the army to avoid trouble only to get in trouble in the army; his sentence was suspended on the condition that he serve as an agent for Space Security. In all his sad, pathetic life, Suz is the only person who’s ever made him feel happy, and he let her slip out of his hands. He’ll do whatever it takes to find her and tell her how she made him feel. But now it appears that he’s lost his chance for good, for there’s no sign of the resistance group which supposedly sent the safe co-ordinates -- and when Pellan hears something approaching, they emerge from the cave to find that they’re surrounded by Daleks...
As the Earth Alliance launches its attack, the Gurian rebels begin to destroy the Dalek saucers on the planet’s surface. Guria may be liberated within hours. Highness and Daughter try to flee from the palace before the Daleks exact reprisals, but the Daleks capture them both and take them to the command centre where the Dalek Commander is co-ordinating the counter-attack. The Daleks are clearly outnumbered, but there are no reinforcements coming and the Commander has been ordered to fight to the last Dalek in order to gain time for the others to evacuate. The Commander broadcasts on all frequencies, ordering the Gurians to lay down their arms; when they fail to respond immediately, he exterminates Highness and threatens to do the same to Daughter. She urges her people to fight on, but the rebels begin to surrender -- and the Dalek Commander gives the order to exterminate them all once they are in custody.
Alby and Pellan are brought to the control platform, where they see the results of the Gurian rebels’ sabotage and realise that the Daleks are losing the battle. They are brought to the command centre with Daughter, who is now herself Highness of Guria -- and to Alby’s shock, the Dalek Commander activates a vid-link to the nearby saucer, allowing him and Suz to see each other for one brief moment before the Daleks cut the link again. As Alby protests, a direct strike from the Earth Alliance forces takes out the control platform. On the Dalek saucer, Suz is separated from Kalendorf and sent to the communications suite for another audience with the Dalek Supreme. Later, the elderly Suz will remember this moment; the way the Dalek Supreme dissected her humanity, probing away at her defenses to find out just what Alby meant to her. But why did the Daleks allow them to see each other in the first place?
Alby wakes days later to find that the Gurians are back in control of their planet -- and that he lost his legs in the attack. New ones have been grafted on, but it will take a while for him to get used to them. Meanwhile, the new Highness questions him about the Angel of Mercy, but he can’t tell her how Suz got mixed up with the Daleks, or why the Daleks allowed them to catch one brief glimpse of each other before separating them again. Before he can puzzle out an answer, the planet is attacked again; the Daleks merely withdrew to a strategic distance to regroup their forces, and have now launched a massive counter-attack. There appears to be no escape, but Highness reveals that a lone Dalek saucer escaped the rebels’ assault, and advises Alby and Pellan to use it to escape. Highness understands what Alby can’t say -- and if she sees Suz, she will tell her that Alby loves her. Alby and Pellan board the saucer, work out how to use its controls, and launch -- but just as they emerge from the atmosphere their saucer is picked up by a retrieval net and tractored aboard an Earth Alliance cruiser. Alby hasn’t figured out the communications system yet, and can’t respond to the Earth forces’ demands that the occupants of the saucer surrender. The Earth soldiers cut through the bulkhead, and as Alby and Pellan try to explain that they’re all on the same side, the soldiers open fire...