|Part 1||Part 2||Part 3||Part 4|
- Part One: Louis was released on September 14th.
- Part Two: Zoey was released on September 21st.
- Part Three: Francis was released on September 28th.
- Part Four: Bill was released on October 5th, at the same time as the DLC for Left 4 Dead and Left 4 Dead 2 The Sacrifice.
The Sacrifice reveals events from the end of Blood Harvest and shows part of the Left 4 Dead Survivors' history just after the start of the Green Flu. The comic is considered to be canon by Valve, including the death of Bill one week after Blood Harvest, as seen in The Passing.
The Sacrifice: Part One covers events from the end of Blood Harvest as the Survivors are fighting their way to the Armored Personnel Carrier sent by the Military. A small flashback revealing the past of Louis during the Green Flu is shown, along with his first encounter with the Infected.
In the present, the Survivors have made it, but their first direct encounter with the Military isn't exactly friendly, as not only are they referred to as "Tango Mikes," but instead of the Echo Safe Zone they thought they were heading to, they are now heading to Millhaven, a location unknown to the Survivors. Upon disembarking, the Survivors are ordered at gunpoint to leave their weapons behind and are marched out of the vehicle where they are met with aggressive military personnel, who immediately do not get along with Francis. A military personnel tells them they are going to "testing," to which Zoey reacts nervously.
The Sacrifice: Part Two continues on from Part One. Two days ago in Millhaven, Sergeant Downey and Lieutenant Mora are discussing the radio silence from command, where word has not been heard from over six days, along with the safety of the compound. In the present day, Louis and Francis are locked up together in a sealed room with independent ventilation, where Francis fails at agitating the military personnel in order to escape. However, they call Louis over, and ask about the mutating Infected, upon which Louis is surprised they have never seen the Special Infected. While Louis is explaining what the Smoker is, Lt. Mora is explaining the Hunter's details to his superior, Major Everly, who does not believe him, nor does he believe that there is a distinction between Carriers and Survivors.
Meanwhile, Zoey and Bill are held under armed guard in a medical examination room. Zoey is coerced into supplying a saliva sample to the doctor, but the threatening behavior involved on the part of one of the guards named Rivera allows Bill to create a distraction which gives Zoey an opportunity to overpower Rivera. However, she releases him when he goes into an inexplicable blind panic, at which point the doctor intervenes and explains the situation. He drops the bombshell that the Survivors are fully infected but asymptomatic Carriers, which means that they have been unwittingly spreading the Infection all over Philadelphia. He also states that no cure is as yet available. Delving deeper into the infection's epidemiology, the doctor explains that the Carrier gene runs on the father's side. Coming right on top of the moral dilemma posed by being a Carrier, Zoey is then psychologically overloaded by a flashback to the time when, two days after the first Infection, she killed her beloved father in the mistaken belief that he would "turn" after having been attacked by her mother. She now realizes that her father was an immune Carrier and that this tragic action was unnecessary. Back to the present, the doctor asserts that he is the only one standing between them and summary execution as infected Carriers. Just after the doctor concludes with a plea that they all help each other escape, a loud alarm goes off in the facility. Lt. Mora has mutinied, relieved Major Everly of command during which process the alarm was tripped. Unfortunately this has enraged all Infected within earshot and the facility becomes the instant focus of their overwhelming attack.
Back in their cell, Francis and Louis who also hear the alarm and know instantly what this foretells. Louis quickly convinces the two soldiers on guard outside the door to not attack a wandering Witch who happens to pass along the corridor at this point. This act of good faith convinces the guards to let Louis and Francis out of their cell and lead them to the armory for weapons. On the way, they encounter a soldier-turned Boomer who Francis is able to dispose of with his bare hands. Unfortunately, the resulting lure of Boomer bile draws Common Infected towards them.
The Sacrifice: Part Three begins with the Infected invading Millhaven, with the two groups reuniting in the armory, where they equip themselves and plan a route to safety. While Bill speaks with Louis and the two soldiers, Annie and Jeff, Zoey talks to Francis about how he is still his joking self, upon which Francis remembers his past. Two days after the first infection, Francis gets in trouble with the law, and is scheduled for jail. However, the outbreak of the Infection spreads, with his ex-girlfriend Sandra being his first encounter with the Infected. When one of his friends Duke kills her and rants about the coming Zombie Apocalypse, Francis realizes the opportunities to be had from such a thing, including the lawless nature of it all.
Back in the present, Lt. Mora loses his mask defending himself from the Infected, upon which his platoon quickly abandon him, leaving him for dead as he is contaminated. Meanwhile, the Survivors along with the doctor and two soldiers fight their way out, hoping to find a train to lead them to the South. Zoey is confused when Bill refuses to change his mind on leaving stragglers behind, although he does not mean his own group with which he has survived with so far. The group runs into an injured―and infected―Lt. Mora who holds them at gunpoint, which Bill quickly disables, but a Tank approaches, killing the soldier, as well as destroying a nearby helicopter carrying Major Everly. With the group using tactics both conventional and unconventional to defeat the Tank, Annie and Jeff bid farewell as they leave to join with a nearby outpost, while the others find a nearby train. The outpost suddenly becomes swamped and overrun with Infected, who see the train in sight. But as they all run, Bill starts the train, leaving the doctor and soldiers who are unable to make it to the train, and killed one by one by the Infected. An upset Zoey shouts at him for leaving them behind as the train continues onwards.
The Sacrifice: Part Four begins with Francis rudely awakened from a dream by Zoey, who is still angry about Bill's decision during the train escape to leave everyone except themselves behind. With arguments in the plans morally dividing the Survivors, it cuts to Bill's past. Two days after the first Infection, Bill is about to undergo surgery in a veterans' hospital when one of the staff turns, with Bill forced to fight against the blackout from anesthesia and kill the Infected before he is killed in turn. Pulling back the panic and fear, Bill escapes the hospital and streets of Infected to make it home. Now equipped in his old army clothing with firearms, Bill is ready to properly face the new threat.
Back to present, while Bill and Louis discuss the Florida Keys, Francis placates Zoey with the fact that while Bill doesn't always do what is right, he still does it for the right reasons. Louis finds a yacht for transport which Bill is against, as he wanted to find a sailboat. Louis excitedly boards only to nearly fall into a room full of Witches, which injure his leg before he escapes. On locating a sailboat, they find it is stocked full of supplies with a dead corpse, which Bill deduces that the sailboat Survivors must have left to raise the bridge for the sailboat to escape from, but didn't make it back. Following this plan, the Survivors take the injured Louis with them, due to the obvious danger of being alone, and fight their way to the bridge, where the button to raise it fails. Bill and Zoey head to the generator to get it working, where Bill tries to apologize, but Zoey cuts him off and says she will follow the plan to head to the Florida Keys. But the sound the generator makes alerts the Infected forcing them to run back to the bridge. As the bridge raises, it is extremely noisy, and alerts hundreds and hundreds of Infected. The bridge grinds to a halt, as four Tanks fight their way through the horde towards the bridge. With the group panicking and morale at rock bottom, Bill leaps off the bridge to fight his way back to the generator to turn it on, drawing three of the Tanks after him while the others, now pushed back to action, cover him and fight off the remaining Tank which stayed behind. Bill manages to turn on the generator but before he can make it back, is mortally injured by a Tank's punch, hurling him into a side room against heavy machinery. Unable to stand up, Bill faces the three Tanks heading for him while lighting a cigarette with a smile on his face. On the raised bridge, Francis wants to go find Bill, but Zoey stops him; if they lower the bridge, all of Bill's efforts for them will be wasted. A dejected Francis can only agree, as Zoey takes up leadership with revised plans: wait it out, remain quiet so the Infected will disperse, take Louis to the sailboat and get away from here. Zoey repeats Bill's motto and words he lived by: "We look after our own."
In the epilogue, Zoey, Louis and Francis are seen on the sailboat heading towards deserted islands in the distance.
- The Survivors' eyes erroneously change colors throughout the comic.
- Francis has no tattoos covering his arms and neck in the comic, nor is his head shaved. The former was likely to reduce the comic artist's workload, while the latter may simply be a style choice.
- In similar vein to the above, Zoey's jacket is unzipped for the majority of the comic, whereas it is always depicted zipped in-game. This was likely to allow the artist to create more dynamic images of Zoey during action sequences, as Bill's jacket is also illustrated to be much more free-flowing than his game model's counterpart.
- The military's approach to the Survivors is inconsistent. At first when speaking to them on the farmhouse radio, the military authorities are surprised and seemingly ecstatic that there are Survivors in need of rescue. However from the time the Survivors are picked up, they are treated as though they are dangerous criminal suspects in the hands of an autocratic police state. They are denied information, assaulted, spoken to harshly, separated from one another and kept in confinement. The initial excitement could likely have been purely that of the soldier who contacted them however, since he is shown to be clearly shaken and sympathetic towards how long the survivors have been in the thick of the apocalypse.
- Although The Sacrifice takes place around the time of Left 4 Dead 2, the Tanks still have hair, like their Left 4 Dead counterparts. No Special Infected introduced in Left 4 Dead 2 are present nor even mentioned in the comic either.
- The Witch in Part 2 wanders through the hallways of the military base, despite the scene taking place at night. It is likely that this detail was simply ignored by the writers of the comic to allow for a more dramatic scene.
- Despite being promoted as going to have over 190 pages, the comic only came with 178.
- The Survivor's weapons randomly change throughout the farmhouse sequence.
- Bill wields an AK-47 in the first part of the comic even though this weapon isn't available in Left 4 Dead. However, this is likely a retcon for Left 4 Dead, like other elements in the comic.
- Francis' pipe bomb ticks instead of beeping.
- The farmhouse sequence erroneously occurs during the night instead of at daybreak.
- At the beginning of the comic when the tanks are about to attack the incapacitated Bill in the generator room, his weapon is empty. But in "The Passing" should another survivor pick it up, it will be fully loaded.
- Since Francis hates water and Louis is incapacitated (and evidently the two of them know little or nothing about boats), one would presume that Zoey has sufficient navigation and ship handling skills to take command of the sailboat.
- The comic is now for sale as part of Valve's book Valve Presents: The Sacrifice and Other Steam-Powered Stories.
- There are small easter eggs in reference to Team Fortress 2 in the comic. At Page 25 of Part 1, as one can see a small action figure of the Heavy on a table. In addition, various scenes throughout the comic have Team Fortress 2 characters hidden within the crowds of zombies.
- A small cameo in reference to the Dead Rising series can be found on Page 101 of Part 3. A poster on the wall depicts artwork of Chuck Greene, the protagonist of Dead Rising 2. This is a nod to Valve's fondness of the series, following on from the Zombie Genocidest achievement in Left 4 Dead. This cameo is only in the original web version of the comic, and is not present in Valve Presents: The Sacrifice and Other Steam-Powered Stories or the downloadable textless version of the comic.