The next step includes gathering information. I keep a notebook ready and have noted down various ideas and snippets over a few months now. The more I browse around I find more and more interesting stuff and I'm almost loosing focus because everything sounds so interesting.

Having a somewhat guided approach to this shouldn't be that bad. Especially when it comes to researching what matters. Here is where a bit oppose the content of the research as proposed. Yes on one hand it is good to keep some references around for the themes you want to incorporate, and it certainly showed maybe some shortcomings about my choices. But I also feel, that looking around what systems are out there and how certain problems (when it comes to the themes or mechanics) have been solved is as important.

Especially when it comes to this different mechanical differences it makes a good starting point for components you can later try out and change by having a catalogue ready of such systems.

This probably will be mostly a link list that I might update from time to time.

Investigation

Everything relating to how investigations are done and how to shape them to make an interesting story.

• Definition of (Criminal) Investigations
• Making Mystery compelling (from a novel writer's standpoint)
• Different obstacles that might occur
• That creepy theme song to every weird mystery (from the excellent Psych episode: Dual Spires - which of course is an homage to Twin Peaks)

Artefacts

Everything relating to artefacts in human history (and fiction)

• Warehouse 13 Artefact List
• List of Mystical Artefacts and Objects
• List of Mystical (Super)powers
• SCP Classification System

Agency

Everything one needs to know how to run a bureaucratic clandestine secret organization

• Bureaucracy in history
• Film Props for creating fake police reports
• How actual clandestine operations work
• Secret Societies in Popular Culture

Underdogs

Everything relating on operating with a small team without special privileges

• Basic rights of civilians and non-european countries
• Detective Tag Teams

Systems and Inspirations

RPG systems and supplements with interesting mechanics

• Tremulus RPG
• FATE Core / FATE Accelerated Edition
• Blades in the Dark
• Year Zero Engine (OGL) (Year Zero Mini)
• Vaesen - based on Year Zero Engine
• GUMSHOE - improved investigation framework
• Perilious Intersections
• Solo Investigator's Handbook - Call of Cthulhu specific
• Ironsworn
• FateLess and SoloFate