SiN takes place in a future where the police forces have been abolished and replaced with security forces, and the evil billionaire Elexis Sinclaire has developed a dangerous mutagen over years of testing, known as U4, which can turn people into monsters. Sinclaire wishes to use her drug to poison the city of Freeport, utilising her security force SiNtek to do so. Protagonist Col. John Blade sets out to stop Sinclaire, aided by his friend and sidekick J.C. Armack who communicates his mission objectives to him and uses his hacking abilities in situations where Blade's brute force is inadequate.
The game includes many (for the time) ground-breaking features, including several different ways to complete missions, drivable vehicles, and a high level of interactivity. This ranged from destroying simple objects also it allows access of computers through a "DOS-like prompt".
A handful of levels deviated from the typical 'shoot everything' mentality of your average first person shooter. One level involved Blade infiltrating a U4 lab as a scientist. He could avoid the security cameras and sneak past scientists at work in order to grab a lab coat and key in order to access the elevators to the sub levels. Although, you could just burst through with guns blazing if you wanted.
Some of the missions could be skipped. There's one such level which was the fantastic missile silo level. Most of the other alternate missions occurred when you completed a secondary objective or failed to complete a primary objective. For example, failing to stop contamination of the primary water supply initiated an additional level where you hurried down the line and shut it off there. The simplest of these involved the first level where shooting an Elexis Sinclaire billboard caused it to crash through the roof of the bank. Once inside the bank you would see the billboard through the roof and the newly damaged fountain flooding the ATM area.
Blade's arsenal includes a fairly typical FPS layout and most weapons lack a secondary fire. Those that are capable of secondary fire have to be switched back and forth between modes.
- Fists - The default weapon of the game, used to punch your enemies.
- Monster's hands - This weapon is used when Blade is injected with U4.
- Concussion gun - A weapon that recharges its ammo. It fires a blue shock wave that will push things out of the way and can be used to jump higher.
- Magnum - Blade's magnum is quite powerfuland head shots will kill most human enemies.
- Shotgun - This causes most things directly in front of the barrel to explode including enemy torsos.
- Submachine gun - This gun uses the same ammo as the Magnum. It is weaker than the magnumbut it fires a lot faster.
- Machine gun - This weapon is versatile, it's stronger than the submachine gun. It's secondary mode uses rockets as grenades. The grenades bounces off of surfaces and explode on targets.
- Spider mines - Small automated mines that skittle forwards slowly.
- Rocket - It packs a punchand you can hold plenty of rockets to keep firing for a while. It also has an alternate fire mode useable with missiles, this allows it to fire remote controlled missiles.
- Plasma rifle - Fires explosive plasma bolts in an arc and have a lighting gun function that fires a continuous beam.
- Quantum Destabilizer - Reduces all enemies in front of you to a fine red mist, however, if the fire button is held down too long, it can kill the player character. It uses the same ammo as the plasma gun but depletes it faster.
- Sniper rifle - A silenced sniper rifle that can blow up the heads of enemies.
- Spear gun - Used mainly in the underwater sections, it fires slow-moving spears that can pin enemies to walls. It is the only weapon capable of firing underwater .
- Silencer - Can be added to the Magnum and Submachine gun to suppress the noise they create.
- U4 - A mutagen that can turn people into monsters.
- Flashlight – Projects light.
- Pentium 166 (200 MHz recommended)
- 32 megs of RAM (64 MB recommended
- Windows 95/98 or NT 4.0 (with Service Pack 3)
- 50 MB of uncompressed hard disk space
- Quad Speed CD-ROM
- 100% SoundBlaster-compatible sound card
- PCI or AGP video card with 2 MB RAM
- Joystick and mouse-supported (3-button mouse recommended)
- Supports network and internet play via TCP/IP
- Internet play via modem requires 100% Windows 95-compatible 28.8 Kbps or faster modem
- Power Mac G3 233 MHz
- 64 MB RAM
- MacOS 8.6
- Pentium 200 MMX with 3D hardware, or a Pentium 2 233 for software-only (Pentium 2 plus 3D hardware recommended)
- 32 MB RAM (64 recommended)
- 70 MB of free disk space
- Linux Kernel version 2.2.x or later (glibc 2.1)
- XFree 3.3 or later (XFree 4.0 recommended)
- OSS/Alsa compatible sound card (/dev/dsp style)