diff --git a/src/sets.lua b/src/sets.lua
new file mode 100644
index 0000000..3cb88a8
--- /dev/null
+++ b/src/sets.lua
@@ -0,0 +1,159 @@
+-- Item sets: matching gear that all share a `set` tag and grants an
+-- escalating stat bonus once enough pieces are worn together at once - a
+-- fixed weapon/armor/ring/bow catalog of named pieces (see Sets.create),
+-- unlike affixes.lua's random roll bolted onto an ordinary base item. The
+-- bonus is read live off however many pieces of a given set the wearer
+-- currently has equipped (Sets.attackBonus/defenseBonus, wired into
+-- combat.lua exactly the way runewords.lua's own live bonus is), so
+-- swapping a single piece out mid-run instantly drops back to a lower
+-- threshold - or none at all - rather than needing an explicit uninstall
+-- step the way a socketed gem or an enchant would.
+
+local Items = require("items")
+
+local Sets = {}
+
+local SLOT_ORDER = { "weapon", "armor", "ring", "bow" }
+
+Sets.catalog = {
+  {
+    key = "ironclad", name = "Ironclad",
+    pieces = {
+      weapon = { name = "Ironclad Greatsword", power = 3 },
+      armor  = { name = "Ironclad Plate", power = 3 },
+      ring   = { name = "Ironclad Signet", attack = 0, defense = 1 },
+    },
+    -- Independent totals, not a stacking ladder: reaching the 3-piece
+    -- threshold replaces the 2-piece bonus rather than adding to it.
+    bonuses = {
+      [2] = { attack = 1, defense = 1 },
+      [3] = { attack = 2, defense = 3, regen = 1 },
+    },
+  },
+  {
+    key = "duskrunner", name = "Duskrunner",
+    pieces = {
+      weapon = { name = "Duskrunner Fang", power = 2 },
+      bow    = { name = "Duskrunner Bow", power = 2, range = 5 },
+      ring   = { name = "Duskrunner Loop", attack = 1, defense = 0 },
+    },
+    bonuses = {
+      [2] = { attack = 1 },
+      [3] = { attack = 3, defense = 1 },
+    },
+  },
+}
+
+Sets.byKey = {}
+for _, spec in ipairs(Sets.catalog) do
+  Sets.byKey[spec.key] = spec
+end
+
+-- Every (set, slot) pairing flattened in a fixed order, mirroring
+-- artifacts.lua's own Artifacts.order: the list a builder placement rolls
+-- a single uniform index into so every piece of every set is equally
+-- likely to turn up on a given floor.
+Sets.order = {}
+for _, spec in ipairs(Sets.catalog) do
+  for _, slot in ipairs(SLOT_ORDER) do
+    if spec.pieces[slot] then
+      Sets.order[#Sets.order + 1] = { set = spec.key, slot = slot }
+    end
+  end
+end
+
+-- Builds the dropped item for `setKey`'s `slot` piece in the same shape
+-- items.lua's own constructors return for that slot, tagged with the
+-- `set` field every function below keys its live bonus off.
+function Sets.create(setKey, slot)
+  local spec = Sets.byKey[setKey]
+  local piece = spec and spec.pieces[slot]
+  if not piece then return nil end
+  local item
+  if slot == "weapon" then item = Items.weapon(piece.name, piece.power)
+  elseif slot == "armor" then item = Items.armor(piece.name, piece.power)
+  elseif slot == "ring" then item = Items.ring(piece.name, piece.attack, piece.defense)
+  elseif slot == "bow" then item = Items.bow(piece.name, piece.power, piece.range)
+  end
+  item.set = setKey
+  return item
+end
+
+-- How many of `entity`'s four equip slots currently carry a piece of each
+-- set it has at least one piece of, keyed by set key. Walks a fixed slot
+-- order rather than pairs() over the entity itself, so the result never
+-- depends on Lua's unspecified table iteration order.
+function Sets.equippedCounts(entity)
+  local counts = {}
+  for _, slot in ipairs(SLOT_ORDER) do
+    local item = entity[slot]
+    if item and item.set then
+      counts[item.set] = (counts[item.set] or 0) + 1
+    end
+  end
+  return counts
+end
+
+-- The richest bonus tier `count` pieces of `setKey` qualify for, and the
+-- threshold it came from, or nil below its lowest threshold.
+function Sets.bonusFor(setKey, count)
+  local spec = Sets.byKey[setKey]
+  if not spec or not count or count <= 0 then return nil end
+  local best, bestThreshold
+  for threshold, bonus in pairs(spec.bonuses) do
+    if count >= threshold and (not bestThreshold or threshold > bestThreshold) then
+      best, bestThreshold = bonus, threshold
+    end
+  end
+  return best, bestThreshold
+end
+
+function Sets.attackBonus(entity)
+  local total = 0
+  local counts = Sets.equippedCounts(entity)
+  for _, spec in ipairs(Sets.catalog) do
+    local bonus = Sets.bonusFor(spec.key, counts[spec.key])
+    if bonus then total = total + (bonus.attack or 0) end
+  end
+  return total
+end
+
+function Sets.defenseBonus(entity)
+  local total = 0
+  local counts = Sets.equippedCounts(entity)
+  for _, spec in ipairs(Sets.catalog) do
+    local bonus = Sets.bonusFor(spec.key, counts[spec.key])
+    if bonus then total = total + (bonus.defense or 0) end
+  end
+  return total
+end
+
+-- Hp `entity` regenerates this turn from any active set bonus that grants
+-- one, summed the same way attack/defense are above.
+function Sets.regenAmount(entity)
+  local total = 0
+  local counts = Sets.equippedCounts(entity)
+  for _, spec in ipairs(Sets.catalog) do
+    local bonus = Sets.bonusFor(spec.key, counts[spec.key])
+    if bonus then total = total + (bonus.regen or 0) end
+  end
+  return total
+end
+
+-- A human-readable "Name Npc" tag for every set currently meeting its
+-- lowest threshold, in catalog order - read by render.lua's status panel
+-- and by nothing that affects game logic.
+function Sets.activeDescriptions(entity)
+  local counts = Sets.equippedCounts(entity)
+  local parts = {}
+  for _, spec in ipairs(Sets.catalog) do
+    local count = counts[spec.key]
+    if Sets.bonusFor(spec.key, count) then
+      parts[#parts + 1] = spec.name .. " " .. count .. "pc"
+    end
+  end
+  if #parts == 0 then return nil end
+  return table.concat(parts, ", ")
+end
+
+return Sets