diff --git a/src/proc/mobject/session/placement-index.cpp b/src/proc/mobject/session/placement-index.cpp
index 294907f5d..a3d4c7420 100644
--- a/src/proc/mobject/session/placement-index.cpp
+++ b/src/proc/mobject/session/placement-index.cpp
@@ -68,8 +68,24 @@ namespace session {
   
   using namespace lumiera;
   
+  LUMIERA_ERROR_DEFINE (NOT_IN_SESSION, "referring to a Placement not known to the current session");
   
   
+  namespace { // implementation helpers
+
+    template <typename MAP>
+    inline typename MAP::mapped_type const&
+    getEntry_or_throw (MAP& map, typename MAP::key_type const& key)
+    {
+      typename MAP::const_iterator pos = map.find (key);
+      if (pos == map.end())
+        throw error::Logic("lost a Placement expected to be registered in the index.");
+      
+      return pos->second;
+    }
+      
+  } // (End) impl.helpers
+  
   
   /* some type shorthands */
   typedef PlacementIndex::PlacementMO PlacementMO; 
@@ -85,7 +101,6 @@ namespace session {
       typedef unordered_map<ID, PPlacement, hash<ID> > IDTable;
       typedef std::tr1::unordered_multimap<ID,ID, hash<ID> > ScopeTable;
       
-//      typedef PlacementMO::ID _PID;
       
       TypedAllocationManager allocator_;
       IDTable placementTab_;
@@ -118,6 +133,18 @@ namespace session {
           return util::contains(placementTab_, id);
         }
       
+      PlacementMO&
+      fetch (ID id)  const
+        {
+          REQUIRE (contains (id));
+          PPlacement const& entry = getEntry_or_throw (placementTab_,id);
+          
+          ENSURE (entry);
+          ENSURE (id == entry->getID());
+          return *entry;
+        }
+      
+      
       void
       clear()
         {
@@ -181,9 +208,13 @@ namespace session {
   
   
   PlacementMO&
-  PlacementIndex::find (ID)  const
+  PlacementIndex::find (ID id)  const
   {
-    UNIMPLEMENTED ("main operation of PlacmentIndex: lookup a Placement by ID");
+    if (!contains (id))
+      throw error::Invalid ("Accessing Placement not registered within the index"
+                           ,LUMIERA_ERROR_NOT_IN_SESSION);              ///////////////////////TICKET #197
+    
+    return pTab_->fetch (id);
   }
     
   
diff --git a/src/proc/mobject/session/placement-index.hpp b/src/proc/mobject/session/placement-index.hpp
index 6cea528a2..b4de007c6 100644
--- a/src/proc/mobject/session/placement-index.hpp
+++ b/src/proc/mobject/session/placement-index.hpp
@@ -68,6 +68,9 @@ namespace mobject {
   
 namespace session {
   
+  LUMIERA_ERROR_DECLARE (NOT_IN_SESSION);  ///< referring to a Placement not known to the current session
+  
+  
   using lib::factory::RefcountFac;
   using std::tr1::shared_ptr;
   using boost::scoped_ptr;