Croteam places Sam’s next conflict with Mental after the earlier game’s ending and takes the fighting to alien worlds.
The Third Encounter begins where Serious Sam: The Second Encounter stopped. Croteam identifies that direct continuation as the game’s place in the story, with Sam taking the conflict toward Mental’s forces. Croteam’s October 21 description of the story connection.
The developer’s Steam description puts the campaign across alien environments, including strongholds and hostile planetary landscapes. Large groups of enemies remain central to its stated combat design, with returning weapons joined by additions to the arsenal. Official game description and development status.
The listed modes include single-player, online co-op, and shared or split-screen play. Those options apply different group arrangements to the same broad premise of fighting through Mental’s forces; the description does not provide a final player count for each mode.
Croteam is developing the game and Devolver Digital is publishing it. The official listing explicitly identifies the project as being in early development, with no release date given.
For the story’s chronology, the confirmed connection is specific: the starting point follows The Second Encounter. The wider route through the new worlds and the details of the confrontation remain only partly described in the current public materials. Croteam’s October 21 description of the story connection. Official game description and development status.