diff --git a/plate-tool-lib/src/lib.rs b/plate-tool-lib/src/lib.rs
index 70231ed..21e5c72 100644
--- a/plate-tool-lib/src/lib.rs
+++ b/plate-tool-lib/src/lib.rs
@@ -3,6 +3,7 @@ pub mod plate;
 pub mod plate_instances;
 pub mod transfer;
 pub mod transfer_region;
+pub mod transfer_region_cache;
 pub mod transfer_volume;
 pub mod util;
 
diff --git a/plate-tool-lib/src/transfer_region_cache.rs b/plate-tool-lib/src/transfer_region_cache.rs
new file mode 100644
index 0000000..bb453a3
--- /dev/null
+++ b/plate-tool-lib/src/transfer_region_cache.rs
@@ -0,0 +1,89 @@
+use std::collections::HashMap;
+use std::sync::{Arc, Mutex};
+
+use crate::transfer::Transfer;
+use crate::Well;
+
+use uuid::Uuid;
+
+#[derive(Debug)]
+pub struct TransferRegionCache {
+    interior: Arc<Mutex<TransferRegionCacheInterior>>,
+}
+
+impl TransferRegionCache {
+    pub fn new() -> Self {
+        TransferRegionCache {
+            interior: Arc::new(Mutex::new(TransferRegionCacheInterior::new()))
+        }
+    }
+
+    pub fn add_overwrite(&self, tr: &Transfer) {
+        let source = tr.transfer_region.get_source_wells();
+        let destination = tr.transfer_region.get_destination_wells();
+        let uuid = tr.id;
+
+        if let Ok(mut interior) = self.interior.lock() {
+            interior.cache.insert(uuid, InteriorWellSlices {
+                source: source.into(),
+                destination: destination.into(),
+            });
+        }
+    }
+
+    pub fn invalidate(&self, tr: &Transfer) {
+        if let Ok(mut interior) = self.interior.lock() {
+            interior.cache.remove(&tr.id);
+        }
+    }
+
+    pub fn get_source(&self, tr: &Transfer) -> Option<Arc<[Well]>> {
+        self.get(tr, true)
+    }
+
+    pub fn get_destination(&self, tr: &Transfer) -> Option<Arc<[Well]>> {
+        self.get(tr, false)
+    }
+
+    fn get(&self, tr: &Transfer, is_source: bool) -> Option<Arc<[Well]>> {
+        if let Ok(interior) = self.interior.lock() {
+            interior.cache.get(&tr.id).map(|x| 
+                if is_source {
+                    x.source.clone()
+                } else {
+                    x.destination.clone()
+                })
+        } else {
+            None
+        }
+    }
+}
+
+impl Clone for TransferRegionCache {
+    fn clone(&self) -> Self {
+        // Clone the interior RC without letting anyone know
+        // shhhh!
+        TransferRegionCache {
+            interior: self.interior.clone(),
+        }
+    }
+}
+
+#[derive(Debug)]
+struct TransferRegionCacheInterior {
+    cache: HashMap<Uuid, InteriorWellSlices>,
+}
+
+impl TransferRegionCacheInterior {
+    fn new() -> Self {
+        TransferRegionCacheInterior {
+            cache: HashMap::new()
+        }
+    }
+}
+
+#[derive(Debug)]
+struct InteriorWellSlices {
+    source: Arc<[Well]>,
+    destination: Arc<[Well]>,
+}