diff --git a/sync/client/memory.go b/sync/client/memory.go
index e7190b4..1b84917 100644
--- a/sync/client/memory.go
+++ b/sync/client/memory.go
@@ -1,22 +1,45 @@
 package client
 
 import (
+	"slices"
+	"sync"
 	"time"
 
 	"go-mod.ewintr.nl/planner/item"
 )
 
 type Memory struct {
+	items map[string]item.Item
+	sync.RWMutex
 }
 
 func NewMemory() *Memory {
-	return &Memory{}
+	return &Memory{
+		items: make(map[string]item.Item, 0),
+	}
 }
 
 func (m *Memory) Update(items []item.Item) error {
+	m.Lock()
+	defer m.Unlock()
+
+	for _, i := range items {
+		m.items[i.ID] = i
+	}
+
 	return nil
 }
 
 func (m *Memory) Updated(kw []item.Kind, ts time.Time) ([]item.Item, error) {
-	return nil, nil
+	m.RLock()
+	defer m.RUnlock()
+
+	res := make([]item.Item, 0)
+	for _, i := range m.items {
+		if slices.Contains(kw, i.Kind) && (i.Updated.After(ts) || i.Updated.Equal(ts)) {
+			res = append(res, i)
+		}
+	}
+
+	return res, nil
 }
diff --git a/sync/client/memory_test.go b/sync/client/memory_test.go
new file mode 100644
index 0000000..c1f451c
--- /dev/null
+++ b/sync/client/memory_test.go
@@ -0,0 +1,60 @@
+package client_test
+
+import (
+	"testing"
+	"time"
+
+	"github.com/google/go-cmp/cmp"
+	"go-mod.ewintr.nl/planner/item"
+	"go-mod.ewintr.nl/planner/sync/client"
+)
+
+func TestMemory(t *testing.T) {
+	t.Parallel()
+
+	mem := client.NewMemory()
+
+	now := time.Now()
+	items := []item.Item{
+		{ID: "a", Kind: item.KindTask, Updated: now.Add(-15 * time.Minute)},
+		{ID: "b", Kind: item.KindEvent, Updated: now.Add(-10 * time.Minute)},
+		{ID: "c", Kind: item.KindTask, Updated: now.Add(-5 * time.Minute)},
+	}
+	if err := mem.Update(items); err != nil {
+		t.Errorf("exp nil, got %v", err)
+	}
+
+	for _, tc := range []struct {
+		name     string
+		ks       []item.Kind
+		ts       time.Time
+		expItems []item.Item
+	}{
+		{
+			name:     "empty",
+			ks:       make([]item.Kind, 0),
+			expItems: make([]item.Item, 0),
+		},
+		{
+			name:     "kind",
+			ks:       []item.Kind{item.KindEvent},
+			expItems: []item.Item{items[1]},
+		},
+		{
+			name:     "timestamp",
+			ks:       []item.Kind{item.KindTask, item.KindEvent},
+			ts:       now.Add(-10 * time.Minute),
+			expItems: items[1:],
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			actItems, actErr := mem.Updated(tc.ks, tc.ts)
+			if actErr != nil {
+				t.Errorf("exp nil, got %v", actErr)
+			}
+			if diff := cmp.Diff(tc.expItems, actItems); diff != "" {
+				t.Errorf("(exp +, got -)\n%s", diff)
+			}
+		})
+	}
+}