diff --git a/app/api/pax8/companies/[id]/route.ts b/app/api/pax8/companies/[id]/route.ts
new file mode 100644
index 0000000..c494a91
--- /dev/null
+++ b/app/api/pax8/companies/[id]/route.ts
@@ -0,0 +1,213 @@
+/**
+ * GET /api/pax8/companies/[id]
+ *   Returns a single PAX8 company's current subscriptions joined to each
+ *   subscription's latest actually-billed order-item line (windowed per
+ *   subscription_id, per D-03 — see 14-RESEARCH.md Pitfall 2), plus a
+ *   summed cost total.
+ */
+
+import { NextRequest, NextResponse } from 'next/server';
+import { requireAuth } from '@/lib/auth-utils';
+import postgresClient from '@/lib/services/postgres-client';
+
+const UUID_RE = /^[0-9a-f-]{36}$/i;
+
+interface CompanyHeaderRow {
+  id: string;
+  name: string;
+  status: string | null;
+  city: string | null;
+  state_or_province: string | null;
+  country: string | null;
+  website: string | null;
+  autotask_company_id: string | null;
+  match_confidence: string | null;
+  match_method: string | null;
+  synced_at: string | null;
+  is_deleted: boolean;
+}
+
+interface SubscriptionRow {
+  subscription_id: string;
+  product_id: string | null;
+  product_name: string | null;
+  sku: string | null;
+  quantity: number;
+  billing_term: string | null;
+  status: string | null;
+  price: string | null;
+  partner_cost: string | null;
+  currency: string | null;
+}
+
+interface OrderItemRow {
+  subscription_id: string;
+  product_id: string | null;
+  sku: string | null;
+  description: string | null;
+  item_type: string | null;
+  start_period: string | null;
+  end_period: string | null;
+  quantity: number | null;
+  unit_price: string | null;
+  line_total: string | null;
+  partner_cost: string | null;
+  partner_cost_total: string | null;
+}
+
+interface SubscriptionBreakdownItem {
+  subscriptionId: string;
+  productName: string;
+  sku: string | null;
+  quantity: number | null;
+  billingTerm: string | null;
+  status: string | null;
+  currency: string | null;
+  latestBilledAmount: number;
+  startPeriod: string | null;
+}
+
+export async function GET(
+  request: NextRequest,
+  { params }: { params: Promise<{ id: string }> }
+) {
+  const { error } = await requireAuth();
+  if (error) return error;
+
+  try {
+    const { id } = await params;
+    if (!UUID_RE.test(id)) {
+      return NextResponse.json({ error: 'Invalid company id' }, { status: 400 });
+    }
+
+    const companyRes = await postgresClient.query<CompanyHeaderRow>(
+      `SELECT id, name, status, city, state_or_province, country, website,
+              autotask_company_id::text AS autotask_company_id,
+              match_confidence::text AS match_confidence, match_method,
+              synced_at::text AS synced_at, is_deleted
+         FROM pax8_companies
+        WHERE id = $1`,
+      [id]
+    );
+    const companyRow = companyRes.rows[0];
+    if (!companyRow) {
+      return NextResponse.json({ error: 'Company not found' }, { status: 404 });
+    }
+
+    let matchedCompanyName: string | null = null;
+    if (companyRow.autotask_company_id) {
+      const matchedRes = await postgresClient.query<{ company_name: string }>(
+        `SELECT company_name FROM companies WHERE id = $1`,
+        [companyRow.autotask_company_id]
+      );
+      matchedCompanyName = matchedRes.rows[0]?.company_name ?? null;
+    }
+
+    // Step 1: current subscriptions for this company.
+    const subscriptionsRes = await postgresClient.query<SubscriptionRow>(
+      `SELECT s.id AS subscription_id, s.product_id, p.name AS product_name, p.sku,
+              s.quantity, s.billing_term, s.status, s.price::text AS price,
+              s.partner_cost::text AS partner_cost, s.currency
+         FROM pax8_subscriptions s
+         LEFT JOIN pax8_products p ON p.id = s.product_id
+        WHERE s.pax8_company_id = $1 AND s.is_deleted = false
+        ORDER BY p.name NULLS LAST`,
+      [id]
+    );
+
+    // Step 2: latest actually-billed order-item line PER subscription
+    // (windowed, not a global MAX — see 14-RESEARCH.md Pitfall 2).
+    const orderItemsRes = await postgresClient.query<OrderItemRow>(
+      `SELECT DISTINCT ON (subscription_id)
+              subscription_id, product_id, sku, description, item_type,
+              start_period::text AS start_period, end_period::text AS end_period,
+              quantity, unit_price::text AS unit_price, line_total::text AS line_total,
+              partner_cost::text AS partner_cost, partner_cost_total::text AS partner_cost_total
+         FROM pax8_order_items
+        WHERE pax8_company_id = $1 AND is_deleted = false
+          AND subscription_id IS NOT NULL
+        ORDER BY subscription_id, start_period DESC`,
+      [id]
+    );
+
+    const latestOrderItemBySubscription = new Map<string, OrderItemRow>();
+    for (const row of orderItemsRes.rows) {
+      latestOrderItemBySubscription.set(row.subscription_id, row);
+    }
+
+    const subscriptions: SubscriptionBreakdownItem[] = [];
+
+    for (const sub of subscriptionsRes.rows) {
+      const orderItem = latestOrderItemBySubscription.get(sub.subscription_id);
+      const price = sub.price !== null ? Number(sub.price) : 0;
+      const quantity = sub.quantity ?? null;
+      // Pitfall 3: never recompute from price*quantity when a line_total exists.
+      const latestBilledAmount =
+        orderItem?.line_total !== null && orderItem?.line_total !== undefined
+          ? Number(orderItem.line_total)
+          : price * (quantity ?? 0);
+      // Pitfall 4: fallback label chain.
+      const productName =
+        sub.product_name || orderItem?.description || sub.sku || orderItem?.sku || 'Unknown item';
+
+      subscriptions.push({
+        subscriptionId: sub.subscription_id,
+        productName,
+        sku: sub.sku ?? orderItem?.sku ?? null,
+        quantity,
+        billingTerm: sub.billing_term,
+        status: sub.status,
+        currency: sub.currency,
+        latestBilledAmount,
+        startPeriod: orderItem?.start_period ?? null,
+      });
+      // Consume this subscription's order item so it isn't re-appended below.
+      if (orderItem) latestOrderItemBySubscription.delete(sub.subscription_id);
+    }
+
+    // Any remaining Step-2 rows belong to tombstoned/unsynced subscriptions
+    // (Pitfall 4) — still surface them as historical breakdown rows.
+    for (const orderItem of latestOrderItemBySubscription.values()) {
+      const lineTotal = orderItem.line_total !== null ? Number(orderItem.line_total) : 0;
+      subscriptions.push({
+        subscriptionId: orderItem.subscription_id,
+        productName: orderItem.description || orderItem.sku || 'Unknown item',
+        sku: orderItem.sku,
+        quantity: orderItem.quantity,
+        billingTerm: null,
+        status: null,
+        currency: null,
+        latestBilledAmount: lineTotal,
+        startPeriod: orderItem.start_period,
+      });
+    }
+
+    const costTotal = subscriptions.reduce((sum, s) => sum + s.latestBilledAmount, 0);
+
+    return NextResponse.json({
+      company: {
+        id: companyRow.id,
+        name: companyRow.name,
+        status: companyRow.status,
+        city: companyRow.city,
+        stateOrProvince: companyRow.state_or_province,
+        country: companyRow.country,
+        website: companyRow.website,
+        autotaskCompanyId: companyRow.autotask_company_id !== null ? Number(companyRow.autotask_company_id) : null,
+        matchConfidence: companyRow.match_confidence !== null ? Number(companyRow.match_confidence) : null,
+        matchMethod: companyRow.match_method,
+        matchedCompanyName,
+        syncedAt: companyRow.synced_at,
+        isDeleted: companyRow.is_deleted,
+      },
+      subscriptions,
+      costTotal,
+    });
+  } catch (err) {
+    console.error('Failed to fetch PAX8 company detail:', err);
+    return NextResponse.json(
+      { error: err instanceof Error ? err.message : 'Failed to fetch PAX8 company detail' },
+      { status: 500 }
+    );
+  }
+}