diff --git a/frontend/src/__tests__/plans.test.ts b/frontend/src/__tests__/plans.test.ts
index 333805fbe..ec2cfe64a 100644
--- a/frontend/src/__tests__/plans.test.ts
+++ b/frontend/src/__tests__/plans.test.ts
@@ -838,6 +838,53 @@ describe('Plans Module', () => {
 
       expect(mockShowToast).toHaveBeenCalledWith(expect.objectContaining({ message: 'Failed to pause purchase: API Error' }));
     });
+
+    test('edit action calls getPlan with plan_id, not the purchase id (#773)', async () => {
+      // The purchase row has id="purchase-1" and plan_id="plan-1".
+      // Before the fix, editPlan received "purchase-1", causing GET /plans/purchase-1
+      // to return 404 and surfacing "Failed to load plan details".
+      (api.getPlan as jest.Mock).mockResolvedValue({
+        id: 'plan-1',
+        name: 'Test Plan',
+        enabled: true,
+        auto_purchase: false,
+        notification_days_before: 3,
+        services: {
+          ec2: { provider: 'aws', service: 'ec2', enabled: true, term: 1, payment: 'all-upfront', coverage: 80 },
+        },
+        ramp_schedule: { type: 'immediate', percent_per_step: 100, step_interval_days: 0 },
+      });
+
+      const editBtn = document.querySelector('[data-action="edit"]') as HTMLButtonElement;
+      editBtn?.click();
+
+      await new Promise(resolve => setTimeout(resolve, 50));
+
+      // Must use the plan FK, not the purchase PK.
+      expect(api.getPlan).toHaveBeenCalledWith('plan-1');
+      expect(api.getPlan).not.toHaveBeenCalledWith('purchase-1');
+      // No error toast should fire.
+      expect(mockShowToast).not.toHaveBeenCalledWith(
+        expect.objectContaining({ message: 'Failed to load plan details' }),
+      );
+    });
+
+    test('edit action with empty plan id is a no-op (defensive guard)', async () => {
+      // Simulate a button whose data-plan-id attribute is missing/empty by
+      // directly injecting a button without the attribute and clicking it.
+      const container = document.getElementById('planned-purchases-list');
+      const btn = document.createElement('button');
+      btn.dataset.action = 'edit';
+      btn.dataset.id = 'purchase-1';
+      // intentionally omit data-plan-id so planId defaults to ''
+      container?.appendChild(btn);
+      btn.click();
+
+      await new Promise(resolve => setTimeout(resolve, 50));
+
+      // getPlan must NOT be called when planId is empty.
+      expect(api.getPlan).not.toHaveBeenCalled();
+    });
   });
 
   describe('resume action for paused purchase', () => {
diff --git a/frontend/src/plans.ts b/frontend/src/plans.ts
index 39a9cb395..b3572038c 100644
--- a/frontend/src/plans.ts
+++ b/frontend/src/plans.ts
@@ -148,7 +148,8 @@ function renderPlannedPurchases(purchases: PlannedPurchase[]): void {
   container.querySelectorAll<HTMLButtonElement>('[data-action]').forEach(btn => {
     btn.addEventListener('click', () => void handlePlannedPurchaseAction(
       btn.dataset['action'] || '',
-      btn.dataset['id'] || ''
+      btn.dataset['id'] || '',
+      btn.dataset['planId'] || ''
     ));
   });
 }
@@ -197,7 +198,7 @@ function renderPlannedPurchaseRow(purchase: PlannedPurchase): string {
         ${canManagePlan && canRun ? `<button data-action="run" data-id="${purchase.id}" class="btn-small primary" title="Run now">▶</button>` : ''}
         ${canManagePlan && isPending ? `<button data-action="pause" data-id="${purchase.id}" class="btn-small" title="Pause">⏸</button>` : ''}
         ${canManagePlan && isPaused ? `<button data-action="resume" data-id="${purchase.id}" class="btn-small" title="Resume">⏵</button>` : ''}
-        ${canManagePlan ? `<button data-action="edit" data-id="${purchase.id}" class="btn-small" title="Edit Plan">✎</button>` : ''}
+        ${canManagePlan ? `<button data-action="edit" data-id="${purchase.id}" data-plan-id="${purchase.plan_id}" class="btn-small" title="Edit Plan">✎</button>` : ''}
         ${canDisablePlan ? `<button data-action="disable" data-id="${purchase.id}" class="btn-small danger" title="Disable Plan">✕</button>` : ''}
       </td>
     </tr>
@@ -221,7 +222,7 @@ function getPlannedPurchaseStatusClass(status: string): string {
 /**
  * Handle planned purchase action
  */
-async function handlePlannedPurchaseAction(action: string, purchaseId: string): Promise<void> {
+async function handlePlannedPurchaseAction(action: string, purchaseId: string, planId = ''): Promise<void> {
   try {
     switch (action) {
       case 'run':
@@ -237,8 +238,13 @@ async function handlePlannedPurchaseAction(action: string, purchaseId: string):
         await api.resumePlannedPurchase(purchaseId);
         break;
       case 'edit':
-        // Open edit modal for the plan
-        await editPlan(purchaseId);
+        // Open edit modal for the parent plan using plan_id, not the purchase id.
+        // The purchase row's data-plan-id attribute carries the plan FK (#773).
+        if (!planId) {
+          console.warn('edit action ignored: missing plan id');
+          return;
+        }
+        await editPlan(planId);
         return;
       case 'disable':
         if (confirm('Disable this plan? The plan will be paused and no purchases will be scheduled. You can re-enable it later from the Plans list.')) {