Most educational games for phones suffer from a recurring design flaw: they underestimate the player’s intelligence. Conventional quizzes tend to offer four obvious multiple-choice options in which elimination by discarding delivers the answer without requiring real reasoning, turning learning into a mechanical and boring routine.

Rastro Frio was developed on the opposite principle: a mobile game of tactical investigation and geographic deduction in a noir style, in which the player acts as an experienced detective on the trail of “Marta, a Turista Fantasma”, deciphering subtle clues about more than 150 cities spread across the planet, without free lists of options.

Transparency: Rastro Frio is a mobile game conceived, designed, and implemented by Jeremias Cardoso, the author of this blog, joining mechanics from classic detective games and modern mobile development.

Deductive mechanics and the clue model

In Rastro Frio, searching for a city requires cultural, geographic, historical, and climatic interpretation. The system operates under a strict resolution rule based on the number of clues the player uses:

  • Pure deduction without free options: the player has to type the name of the suspected city or locate it directly on the interactive world map. There is no prior list of cities for a mere guess.
  • The 1/2/3 rule: getting the destination right with only 1 clue yields an immediate capture and the maximum score bonus; with 2 clues the target escapes, but the streak of correct answers extends; with 3 clues a witness hands over a ciphered clue for the next stop; a wrong guess consumes precious days on the search calendar and makes the trail go cold.
  • Informant help at a strategic cost: consulting local informants for a restricted list of five suspected cities consumes two days of the detective’s available time, forcing the player to manage that time with discipline.

Additional challenges: ciphers and interrogations

To enrich the noir atmosphere and exercise different facets of logical reasoning, the game incorporates complementary investigative mechanics:

  • Ciphered notes: clues transmitted by witnesses arrive encoded with classic substitution ciphers (Caesar cipher). The player can pay investigation days to decode the message automatically, or decipher the puzzle mentally to save time.
  • Check interrogations: on completing the capture of a leg, the detective answers quick questions about real data for the locality (capital, continent, time zone, or hemisphere), gaining extra days on a correct answer or losing time on an error.

Architecture: Flutter, offline-first, and immutable integrity

Developed for Android smartphones, the game was structured on good mobile software engineering practices:

  • Flutter and Dart: a native interface with fluid rendering, a high-contrast dark palette (noir theme), and custom display fonts.
  • 100% offline-first operation: the entire collection, with more than 150 cities and hundreds of detailed clues, lives locally in immutable data structures validated by integrity tests.
  • A pure, testable game engine: the core of the rules logic (score calculation, day progression, and random drawing of stages) is completely decoupled from the graphical interface, guaranteeing mathematical reproducibility in unit-test suites.

Rastro Frio shows how the union of an engaging narrative, rigor in data curation, and authentic deductive mechanics creates a mature and stimulating educational experience.

Na Trilha da Herdeira: the same premise in tactical turns

Update note (October 29, 2026): this section incorporates the post about Na Trilha da Herdeira, published on September 17, 2026, which no longer exists as its own page.

Na Trilha da Herdeira is another mobile investigation game by the author, still being implemented. The premise resembles that of Rastro Frio — chasing someone around the world by deducing each destination — but the structure is that of a turn-based tactical game with RPG progression: the player follows the heiress Xenia Alvarenga along a trail of puzzles.

The design rests on four rules:

  1. Deduction, not luck: the clues are resolved by logic, with no hidden die deciding success.
  2. The world as a reward: even when wrong, the player sees real data on geography, history, and relief.
  3. Visible mastery: as the detective rises in rank, from 1 to 10, the clues get harder and the tool panel grows.
  4. Respect for time: stages of three to six minutes, with no mandatory repetitive task and no purchased advantage.

Each round is a turn with a budget of Action Points (AP). Analyzing the clue costs 1 AP; consulting a specialized informant, such as someone in climate and relief, numismatics, history, or regional gastronomy, costs 1 AP and funds; higher ranks unlock a time-zone radar and a continental filter; traveling costs 0 AP and ends the turn with the deduction. Getting it right on the first try yields morale and reputation seals, which open new branches of the story.

The game uses the Godot 4.7.2 engine, with C# and GDScript. Scenes and nodes separate the narrative engine, the experience calculation, and the interface; the data for cities, routes, informants, and dialogue live in validated structures; and everything runs offline on the phone.

Sources

  • Patterns and conventions for deductive investigation games and clue mechanics — The Art of Game Design: A Book of Lenses (game design reference), verified on 2026-09-16.
  • Game Design Document (GDD) specification, geographic data collection, and source code of Rastro Frio — internal project repository (the author’s internal measurement), verified on 2026-09-16.
  • Game design principles, action-point economy, and tactical progression of Na Trilha da Herdeira — Rules of Play: Game Design Fundamentals (Katie Salen and Eric Zimmerman, MIT Press), verified on 2026-09-17.
  • Game design document and turn-balancing matrix of Na Trilha da Herdeira — internal project repository (the author’s internal measurement), verified on 2026-09-17.