An unknown amount of time before the events of Serious Sam 3: BFE, a massive portal opens in Tunguska, Russia which serves as a bridgehead for Mental’s forces to invade Earth. As the whole planet fights the alien invasion, a unit from the Earth Defense Force led by Serious Sam is sent by General Brand to Rome and meet Father Mikail, a priest who claims to have found some clues leading to the Holy Grail which according to him, is a powerful alien artifact hidden inside the Ark of the Covenant. However, the team is forced to abandon the city once it is overrun by Lord Achriman, one of Mental’s generals and his army. In order to get back to the city, Sam and his companions retreat to Pompeii where they use a seismic device to trigger an eruption on Mount Vesuvius that disrupts Achriman’s air forces, but in the occasion, Jones, one of Sam’s companions is killed by one of the alien monsters.
Upon returning to Rome, Sam follows Father Mikail’s instructions and sets to the Vatican where he retrieves a book that reveals the location of the Grail on an abandoned church in Carcassonne, France. Once at the city, Sam is confronted by Achriman, who kills Kenny, a new recruit, in front of him and flees. With help from the local resistance, Sam and his friends arrive at the church where they confront and defeat Lord Achriman, whom Sam kills personally to avenge Kenny. Outside the church, Father Mikhail begins to express doubt the Grail is really what is hidden inside the Ark of the Covenant. Inside the church, Father Mikail uncovers the Ark, which actually contains a golden scepter with the figure of a snake wrapped around it (likely Aaron’s Rod). General Brand appears and reveals himself as a traitor, intending to offer the artifact to Mental as a gift. He uses the artifact to transform into a monster before killing Father Mikail and capturing Sam along the rest of his team.
Awakening inside Brand’s transport plane, Sam escapes by parachute and reaches an abandoned oil platform in the Arctic where he obtains a boat and departs to Tunguska after him. On the way there, Sam is assisted by himself from an alternate dimension who provides him with a snowmobile so that he can reach Brand before he escapes through the portal. Once arriving at the portal site, Sam learns that his friends also escaped and they join a large scale battle between the EDF and the alien forces. Brand captures Sam and offers both him and the artifact as a gift to Ugh-Zan VI which is one of Mental’s most powerful warriors, but the alien rejects him. With help from his friends, Sam kills Ugh-Zan VI with the artifact and Brand is strapped into an ICBM which is launched into the portal, destroying it.
After the battle, Sam and his remaining friends celebrate while remembering their lost companions and Sam indicates that their next mission will be in Egypt, leading to the events of Serious Sam 3: BFE. In a post-credits scene, the alternate-reality-Sam meets an old lady whom Sam met in Rome and asks for her help.
Development
Development of Serious Sam 4 began in October 2012.[2] The game was confirmed in June 2013, when the website Humble Bundle launched a “Humble Weekly Sale” containing several past games from the Serious Sam series to help fund the game.[3][4] While playtesting the game’s “jammer” feature—a movable device that could disable objects in a certain radius—the development team devised that this component and further prospective mechanics would better fit a different type of game, which was developed as The Talos Principle and released in 2014.[5][6] In September 2015, The Talos Principle co-writer Jonas Kyratzes and his wife, Verena, were announced as the screenwriters for Serious Sam 4.[7]
Serious Sam 4 was announced under the name Serious Sam 4: Planet Badass in April 2018, during the opening of the Reboot Develop 2018 conference in Croatia, with a teaser trailer.[8] One level was demonstrated behind closed doors at E3 2018 that June.[9][10] At the time, the game was planned to launch in 2019.[10] In May 2020, Serious Sam 4 was re-announced without the Planet Badass subtitle and with a release window of August 2020 for Microsoft Windows and Stadia.[11][12] According to developers, the Planet Badass title, which had borne out from the game’s plot of a few Earthlings fighting against invading forces, was dropped as localizing this part of the title to other languages was impossible to do.[13]
The game was later delayed to 24 September.[14] Due to an exclusivity deal with Stadia, versions for PlayStation 4 and Xbox One were postponed to early 2021.
