Marathon: How to Complete Parasitism 4 in One Run – Dire Marsh Guide

The Short Answer

Parasitism 4 is a Sekiguchi three-stop run on Dire Marsh, and all three objectives have to land in a single raid. Download research clearance from the terminal in the second-floor southern office of the Maintenance POI on the map’s southern edge — finishing that download locks the doors and spawns UESC, so top up before you start it. Then take the exterior ladder up Bio-Research, break a second-floor window, and use the orange wall dispenser on your left; it drops the Synthsilk Sample on the floor, which you must physically pick up. Finally deliver it to the DCON on the outskirts of Greenhouse. Clean solo run: about 12 minutes.

Dire Marsh in Season 2 (Verified July 2026)

Marathon is on Season 2: Nightfall, live since 2 June 2026 and running to 22 September 2026, 17:00 UTC. Current build is Update 1.1.5 (21 July 2026), which also opened the limited-time Vault Breaker PvE mode in Cryo Archive through 4 August.

What changed for anyone routing Dire Marsh:

• Night Marsh. Nightfall added a nighttime variant of Dire Marsh — same geography, built around darkness and drastically reduced visibility, playing closer to survival horror.
• 90-minute rotation. Both versions ran simultaneously for the season’s first week, then began alternating availability every 90 minutes. You cannot count on the day version being queueable at any given moment.
• Contracts mostly carry over. Bungie’s Season 2 material indicates existing Dire Marsh contracts generally function on Night Marsh too, with some new MIDA and Traxus contracts being Night-exclusive.
• Dire Marsh is in the Duos Queue, the new daily-rotating pair queue alongside Perimeter, Night Marsh and Outpost.

Honest caveat: the 1 June wipe cleared Runner level, faction levels and upgrades, contracts, Credits and Vault contents, and Bungie reworked progression for Nightfall without publishing a per-contract changelog. Only the first Priority Contract per faction carried over. So we cannot independently verify this chain’s exact current name and numbering in Update 1.1.5. The map layout — the POIs, the ladder, the dispenser, the DCON — is unchanged, and that is the part that costs you runs.

Prep: This Is a One-Raid Contract

Because everything has to happen in one session, Parasitism 4 rewards route discipline over gunplay.

• Track the contract. Confirm it is active under Sekiguchi so objectives appear on your HUD.
• Mobile mid-range kit. You are covering three POIs. Prioritise movement and ammo efficiency over a heavy setup.
• Ammo and meds over grenades. The Maintenance ambush is the one fight you cannot skip, and you want to walk out of it healthy.
• Contract-runner mindset. If a fight does not directly advance an objective or unstick you, avoid it.
• If Night Marsh is the live rotation, expect the Bio-Research ladder approach to be far safer than usual — nobody sees you climbing — but the Maintenance-to-Bio-Research leg to be much more dangerous, because you will not spot a held angle until you are inside it.

Step 1: Research Clearance at Maintenance

Finding it

Maintenance is a named POI on the southern edge of Dire Marsh. Mark it the moment you drop. If you spawn far north, do not detour to loot — go straight south and get the dangerous part done while the lobby is still spreading out.

Look for the large industrial main building with multiple entrances. Approach from the west or southwest to stay off the lines that players hold from the towers and catwalks.

Reaching the terminal

• Enter through any ground-level door.
• Take a staircase or interior ramp to the second floor.
• Hug the southern side of the floorplan and look for an enclosed office — not the open catwalks or storage bays.

The terminal is inside that southern office and hard to miss once you are in the right room.

Surviving the ambush

This is the part that ended my first two attempts. As soon as the download completes, nearby doors lock and UESC spawn inside and around the building — and in some runs a tougher unit shows up that plays like a mini-boss. You cannot sprint out and skip it; the doors stay locked until the spawns are cleared.

Treat it as a mini defence event:

• Reload and slot your meds before you start the download, not after.
• Put your back to a wall where you can watch the office entry points.
• Use the doorway as a funnel. Let them come into a narrow angle instead of fighting in open corridors.
• Listen. Enemies announce themselves before they turn the corner.

Once the locks disengage, confirm the objective ticked before you leave. If it did not, you either hit the wrong terminal or the download was interrupted.

Step 2: Synthsilk Sample at Bio-Research

Getting there

Bio-Research sits toward the more central part of Dire Marsh. Ping it so you keep a nav marker, and take indirect, cover-heavy paths — weave between structures, use low walls, and avoid long exposed causeways. This leg is where I get third-partied most. If you hear sustained gunfire, route wide around it rather than through.

Two ways in

• Ladder and window (my default). Climb the exterior ladder up the side of the building, break one of the second-floor glass windows, and hop in. It drops you almost on top of the dispenser and keeps you off predictable ground-floor chokepoints.
• Stairs (safer once the area is cleared). Ground-floor door, interior stairs, follow your tracker to the second-floor lab.

The dispenser trap

Coming in through the broken window, look immediately left for an orange wall-mounted dispenser. Interact with it and it plays an animation, then spawns the Synthsilk Sample on the floor.

This is where people lose the run: the animation is not the objective. You have to look down, interact again to pick the sample up, and confirm it is in your inventory before you move. I sprinted off twice assuming it auto-completed.

Step 3: Deliver at the Greenhouse DCON

There are several DCONs on Dire Marsh; the closest and safest after Bio-Research is on the outskirts of the Greenhouse POI. Ping Greenhouse, then route slightly wide — players love fighting in and around it.

DCONs sit out in the open but near cover, and read as small terminal-like field stations. If you are not sure what you are looking for, our DCON locations guide maps them out.

1. Interact with the DCON to open its interface.
2. Switch to the delivery panel if needed.
3. Move the Synthsilk Sample into the send-back slot.
4. Confirm, and wait for the contract to tick complete before you move.

Once it transmits, all three objectives are satisfied and the contract is banked. Your priority flips to survival — extract to keep your gear, or keep playing the raid if you are confident.

Route Timing

Window	What you should be doing
0–3 min	Drop, beeline south to Maintenance, minimal looting
3–6 min	Second-floor southern office, download, survive the UESC spawn, restock from fallen AI
6–9 min	Move to Bio-Research, ladder and window entry, grab and pick up the sample
9–12 min	Greenhouse outskirts DCON, deposit, then extract or keep playing

Under 10 minutes in a quiet lobby, 15–20 in a contested one.

Mistakes to Avoid

• Treating it as multi-run. Leaving after Maintenance does not bank anything. All three steps, one raid.
• Starting the download unprepared. Half a mag and no meds against a locked-door spawn wave is a wipe.
• Skipping the sample pickup. The dispenser animation is not the objective.
• Over-looting between POIs. Contract first, loot after.
• Taking straight lines. The direct path between POIs is the one everyone watches.

What Comes Next

Parasitism 4 is a good skills test for the rest of Sekiguchi: reading Dire Marsh under pressure, chaining POIs without getting bogged down, and managing terminals that trigger spawns and door locks. The standing and materials it pays feed straight into faction upgrades — the best faction upgrades guide covers which nodes deserve your Credits after a wipe, and if you keep dying on the way out rather than at the objectives, six survival tips for longer raids is the one to read next. The Marathon hub has our full patch, map and contract coverage.

FAQ

Can I split Parasitism 4 across multiple raids?

No. All three objectives must be completed in a single Dire Marsh run. Leaving after Maintenance banks nothing toward it.

Why did the doors lock after I downloaded the clearance?

That is the intended trigger — completing the download locks nearby doors and spawns UESC inside and around the building. Clear them all and the locks disengage.

I used the dispenser but the objective did not complete. What did I miss?

The pickup. The dispenser drops the Synthsilk Sample on the floor in front of it; you have to interact again to collect it and confirm it is in your inventory.

Does this run work on Night Marsh?

Bungie’s Season 2 material indicates existing Dire Marsh contracts generally function on the night variant, with some new contracts being Night-exclusive. The POIs are identical — visibility is the difference, which makes the ladder entry safer and the open-ground legs far riskier.