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Solving interdimensional crimes

Designing the investigation system for Double Cross

One of the most exciting moments in pre-production for Double Cross was when we decided to try the interdimensional police as the game's setting. It's a setting that opened for so many possibilities! Worlds with different mechanics, character with unique looks, and a huge amount of potential stories to be told.

It wasn't until a few months later that Alex, our CEO and Double Cross's creative director, asked me if I had an investigation system ready for a pitch due a few days later. I was confused at first, but soon understood that an investigation system was the piece that we were missing. After all, we were already planning a system of non-linear platforming levels to represent a variety of locations in the multiverse, and were already designing a combat system that'd let players confront and capture criminals and evildoers. But we had nothing to showcase the detective work and mystery solving aspect of our main character's job, special RIFT agent Zahra Sinclair. And having a cool investigation system would add something unique to the action game we were developing.

  Part of the mock-up I put up together for the pitch

Part of the mock-up I put up together for the pitch

I quickly designed the first iteration of the investigation system. To do that, I took the detective board idea and thought of a mechanic that would use one.

In this first iteration, as you beat the game's levels and talk to certain NPCs you would find items or notes that worked as clues, like you would in Ace Attorney. While in the game's hub level at the RIFT HQ, you could access Zahra's detective board and place clues alongside pictures of characters you'd met and locations you'd visited. There, you had a limited amount of red strings that you could use to connect clues, profiles and locations.

If an NPC's profile was connected to the right clues or locations with a red string, new dialogue options would be available when talking to them, and you'd be able to unlock further clues, areas, or lore. That successful dialogue changed the red string into a green one, meaning that part of they mystery was solved. Eventually, getting a green string between the masked villain and one of the other RIFT agents would reveal the traitor and unlock the game's final level.

  Figuring out this villain's identity is at the core of Double Cross's investigation system

Figuring out this villain's identity is at the core of Double Cross's investigation system

The board would be a nice visual representation of the player's progress, as well as a way of helping understand the complex, non-linear, multi-layered plot we were planning. Furthermore, it felt like a great way of having players fulfill the detective fantasy.

The first iteration worked well for the pitch, but as we went deeper into its details we realized that the system was excessively complicated and didn't really streamline towards the goal of figuring out who the traitor was. So Design and Narrative started to work together in designing a new investigation system. For the next three weeks one of the designers and myself turned our computers off, sat on a couch, and started crafting a paper prototype that included the characters, locations and clues for the game.

For the new system, we kept gathering clues throughout the game's levels, but changed what you do with them. Instead of physically connecting stuff in a board, you would make a 'deduction' by connecting a clue and a character profile with a phrase, a system inspired by Detective Grimoire's.

  I recommend taking a look to Detective Grimoire to anyone designing a game with any kind of investigation system

I recommend taking a look to Detective Grimoire to anyone designing a game with any kind of investigation system

A further simplification we had in this system was that each character only had one clue tied to them. Once you had used a clue properly, you would be able to get some evidence that served as an alibi to the character, removing them from the list. You repeated this until you were only left with three suspects. At that point, the final deduction was a more complicated version of the same system, having to tie three clues to a character through several phrases. Doing it successfully would unlock the final part of the game.

As soon as we had the paper prototype ready, we started bringing our co-workers one by one to play through it. We observed where they got stuck, what they found too easy or difficult, listened to their feedback, and slowly improved the prototype after each playtest session.

Eventually, the investigation system underwent several changes, such as dividing the characters in 'profiles' for RIFT agents and 'case file' for the villains. This is a summary of how it worked:

  1. Talk to NPCs to get their Profiles and Case files

  2. Defeat levels to get Clues (or Evidences in boss levels)

  3. Connect a Profile and the right Clue using one of the six available phrases to get Evidences

  4. Connect a Case file and the 3 right Evidences to unlock a boss level

It wasn't perfect, but it was fun and it involved some great character interactions. Our schedule was already pretty tight without spending more weeks working on this system, so we decided to move forward with this.

  The paper prototype was essential in developing this system, as well as a source of jokes and character ideas that would go on to the final product

The paper prototype was essential in developing this system, as well as a source of jokes and character ideas that would go on to the final product

After leaving it be for some weeks, we came back to it once it was actually time for our coders to implement it. Reviewing it again, Design realized that it was too complicated and many players might not enjoy stopping their platforming to go through something like that. So we decided to start removing some of the intrincacies and simplify the system.

First of all, after some discussion we tried removing the Detective Grimoire-style phrases, which were considered an unnecessary step to verify if players actually understood the connection between the clue and the character. The result felt less frustrating in playtesting, so we decided to keep the phrases out.

We also decided to have Zahra show the clues directly to the characters, instead of connecting them to profiles. Besides removing the step of having to talk to a character after making the right deduction, this allowed us to write some funny or insightful reactions to the wrong clues, which ended up being a great addition.

  You can even get some Achievements by showing wrong clues to certain NPCs

You can even get some Achievements by showing wrong clues to certain NPCs

Finally, several weeks later, we removed the step of assigning evidence to case files, which removed an entire tab from the menu and greatly simplified the process. This is how the simplified investigation system works:

  1. Defeat levels to get Clues (or Evidences in boss levels).

  2. Show the right Clue to a character to get an Evidence.

  3. Evidence is automatically assigned to a Case file that you have from the beginning.

  4. Talk to the Commissioner once a Case file is complete to unlock a boss level.

And that's pretty much the system you will find in the final product!

I still feel like some of the previous iterations could have been really interesting on their own, and I wouldn't mind revisiting them for some other project. But the simplified system works really well in combination with the rest of the game. It's simple and it goes straight to the point, but it still feels unique in an action-platformer, lets you experience the detective fantasy, and it's a key feature of the game that pairs up well with the other mechanics.


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Unai Cabezón worked as Narrative Director and Programmer in Double Cross, and as Technical Director in Runbow.

He loves running tabletop roleplaying campaigns and discussing the old Star Wars Expanded Universe.