Thief is a reboot of the Thief series and throws away most of the lore. The game starts when Garrett, a master thief, is on a job with his former apprentice Erin. They run into a mysterious ritual from a faction loosely reminiscent of the Mechanists, and due to unfortunate happenings Erin falls right into the middle of it. Garrett blacks out for a year and awakens in the city which has changed to a fascist regime in the meantime. Now Garrett has to use his thieving skills to find out what is going on (the common people are affected by a strange disease) and eventually stop the usual conspiracy. The basic structure is similar to Deadly Shadows : There is a semi-open city hub structured into various districts. Just like in the predecessor, those are divided in loading screens and gradually open up over the course of the game. These can be freely explored until starting a self-contained mission at the designated point. The main difference to the previous Thief games: instead of sandbox levels, the design is completely modular and can be compared to the Clocktower level in Deadly Shadows . The set-pieces may be relatively open in itself and offer various ways to deal with obstacles or reach new areas, but they also have hidden dangers.
Between missions, Garrett can find much loot in the city by just moving around and keeping his eyes open. However, the most lucrative is to take optional side missions. Here Garrett has to retrieve a certain object - usually it is just a quick burglary within the city, but sometimes they are real self-contained missions. Of course there is a useful usage for money: visiting a shop and stock up on equipment. The obvious choices are depleting resources like Garrett's trademark arrows which can be used for many tasks, e.g. regular arrows for distracting guards or water arrows to extinguish light sources, food items to heal, or smoke bombs.
Garrett also has two magical abilities to his disposal: The swoop move works similar to blink and allows him to quickly move forward. Focus slows down time and has several useful perks, e.g. faster lockpicking, easier combat or showing all loot in the area. Those perks have to be unlocked with focus points which are also bought with money.
One of the game's special features are the difficulty modes. While there are the usual three standard types - the highest does not allow for kills or civilian knockouts - the player can also add several other difficulty options, e.g. disabling focus, more expensive resources, slower movement, no kills or knockouts, no quicksave or permadeath.
Besides the main campaign, there is also a challenge mode. This mode re-uses some of the game's mission areas and adds special objectives. The goal is to get as high a score as possible on leaderboards.
The PlayStation 4 version uses the DualShock 4 gamepad's light bar to emphasize the effect of being in the shadow (with a dimmed dark blue) or exposed to the light (with a bright white).