Doctor Who
S20E4
· Arc of Infinity Part 4

Doctor Nyssa fight Ergon in pump room

The Doctor races to sabotage Omega’s fusion booster but pauses to explain Amsterdam’s geography to Nyssa, revealing the booster’s Gallifreyan origin. As he works, an Ergon materializes—Omega’s failed psychosynthesis—and fires at point blank range while the Doctor bends down. Nyssa’s warning shouts snap him from the danger long enough for him to force the weapon from the Ergon’s grip and pin it during a brutal struggle. When it begins to strangle him, Nyssa seizes the chance, fires its own weapon, and destroys the creature in a flash of decisive action. The Doctor reclaims the weapon and rushes them both back to the crypt just as Omega’s TARDIS reappears, deepening the chase and heightening the stakes before their direct incursion to confront the renegade Time Lord.

Plot Beats

The narrative micro-steps within this event

4

The Doctor identifies the fusion booster from Gallifrey and begins to sabotage it, revealing his plan to stop Omega.

determination to urgency ['pump room']

The Ergon attacks the Doctor and Nyssa, leading to a struggle that puts the Doctor in danger.

urgency to fear ['pump room']

Nyssa saves the Doctor by picking up the Ergon's weapon and firing it, destroying the Ergon.

fear to relief ['pump room']

The Doctor and Nyssa proceed into Omega's TARDIS, ready to confront Omega directly.

relief to determination ['crypt']

Who Was There

Characters present in this moment

3
The Fifth Doctor
Time Lord
 primary

Focused urgency lurking beneath dry conversational ease as the immediacy of violence intrudes on his technical focus

Hunched over the pump room’s booster, the Doctor rapidly attaches a jury-rigged sabotage device while delivering a real-time geography lecture to Nyssa and simultaneously reacting to the Ergon’s sudden assault, pivoting from technical precision to desperate hand-to-hand struggle to save himself.

Goals in this moment
  • • Sabotage Omega’s fusion booster before it completes its destructive cycle
  • • Survive the Ergon’s ambush and neutralize the immediate threat
Active beliefs
  • • Every moment counts in preventing temporal catastrophe
  • • Close coordination with allies is the only reliable counter to Omega’s erratic weaponry
Character traits
Multi-tasking under pressure Quick reflexes Conducting patter even under lethal threat Adaptive improvisation
Follow The Fifth …'s journey
Nyssa
Companion of the Doctor
 primary

Alert vigilance sharpened by sudden danger, translating into swift, controlled aggression when the moment demands it

Initially alert observer, Nyssa shouts a warning as the Ergon materializes, then scoops up its discarded weapon and fires a decisive shot that eliminates the creature at close range, before sprinting with the Doctor back into the crypt to regroup.

Goals in this moment
  • • Protect the Doctor from the Ergon’s immediate attack
  • • Contribute directly to neutralizing Omega’s creations
Active beliefs
  • • The Doctor’s mission cannot be allowed to fail
  • • Direct intervention, even against monstrous odds, is morally obligatory
Character traits
Situational awareness under pressure Decisive action in crisis Immediate tactical response Loyal ally following instinct to protect
Follow Nyssa's journey
Ergon
primary

Programmed aggression with no discernible internal conflict

Materializing abruptly from Omega’s TARDIS into the confined pump room, the Ergon raises its angular plasma weapon and fires at the low-profile Doctor, then resorts to strangulation during a brutal physical struggle before being destroyed by Nyssa’s counterfire.

Goals in this moment
  • • Eliminate the Doctor to protect Omega’s fusion booster
  • • Fulfill its creation programming despite manifest inadequacies
Active beliefs
  • • Obedience to Omega’s will constitutes purpose
  • • Violence is the only valid expression of function
Character traits
Sudden, grotesque apparition Single-minded lethal aggression Mechanical brutality in close quarters Futile continuation of Omega’s failed experiments
Follow Ergon's journey

Objects Involved

Significant items in this scene

2
Fusion Booster Element

The Doctor’s improvised sabotaging device, cobbled from scavenged parts, is actively engaged against Omega’s fusion booster while he delivers his Amsterdam geography monologue, highlighting the improvised yet precise nature of his assault.

Before: Scuffed alloy casing with exposed wiring, held in …
After: Temporarily abandoned during the Ergon struggle, reclaimed once …
Before: Scuffed alloy casing with exposed wiring, held in the Doctor’s hands and clamped to the booster’s housing.
After: Temporarily abandoned during the Ergon struggle, reclaimed once the creature is neutralized and taken into the crypt.
Olvir's Sidearm

The angular Ergon weapon is fired at point-blank range while the Ergon attempts to overwhelm the Doctor, seized and wrestled from its grip, then discharged by Nyssa to obliterate the creature, before being retrieved by the Doctor for continued use.

Before: Clutched in the Ergon’s webbed grip, plasma aperture …
After: Seized by the Doctor post-vaporization, its energy circuits …
Before: Clutched in the Ergon’s webbed grip, plasma aperture glowing dangerously.
After: Seized by the Doctor post-vaporization, its energy circuits still intermittently active, taken into the crypt alongside Nyssa.

Location Details

Places and their significance in this event

1
Time Lord Capitol Core

The utilitarian, steam-hiss environment of the pump room becomes the deadly cockpit of an ambush, its narrow confines amplifying the visceral immediacy of the Ergon’s overwhelming attack and the Doctor’s desperate physical resistance.

Atmosphere Tense and claustrophobic with mechanical hiss and latent threat, broken by sudden shouts and the …
Function Active battleground for close-quarters survival and tactical defense against an immediate lethal force
Symbolism Represents the cramped, vulnerable intersection where Time Lord ingenuity confronts Omega’s deranged persistence in a …
Access Limited by the chamber’s narrow access and the TARDIS doorway looming as potential egress
Flickering overhead lighting casting jagged shadows Hissing steam from ruptured piping adding rhythmic menace

Narrative Connections

How this event relates to others in the story

What this causes 3
Causal

"The Doctor’s sabotage of the fusion booster inside the crypt (Act 2) directly leads to the confrontation in Omega’s TARDIS (Act 3), where he reveals the explosion to Omega and Tegan, causing Omega to drop his weapon."

Omega’s desperate final stand crumbles
S20E4 · Arc of Infinity Part 4
Causal

"The Doctor’s sabotage of the fusion booster inside the crypt (Act 2) directly leads to the confrontation in Omega’s TARDIS (Act 3), where he reveals the explosion to Omega and Tegan, causing Omega to drop his weapon."

Doctor seeks matter converter in ruins
S20E4 · Arc of Infinity Part 4
Causal

"The Doctor’s sabotage of the fusion booster inside the crypt (Act 2) directly leads to the confrontation in Omega’s TARDIS (Act 3), where he reveals the explosion to Omega and Tegan, causing Omega to drop his weapon."

Doctor destroys Omega on the pier
S20E4 · Arc of Infinity Part 4

Part of Larger Arcs

Nyssa’s internal conflict between her loyalty to the Doctor and her fear of reckless sacrifices that may harm their mission

Key Dialogue

"DOCTOR: Yes, perfect."
"DOCTOR: Nyssa!"
"DOCTOR: Nyssa! Fire, Nyssa!"