diff --git a/twiq/Cargo.lock b/twiq/Cargo.lock
index 926bfc1f..bc5449b3 100644
--- a/twiq/Cargo.lock
+++ b/twiq/Cargo.lock
@@ -868,7 +868,12 @@ dependencies = [
 name = "query_handler"
 version = "0.0.0"
 dependencies = [
+ "anyhow",
+ "async-trait",
  "domain",
+ "thiserror",
+ "tokio",
+ "tracing",
 ]
 
 [[package]]
@@ -1201,18 +1206,18 @@ dependencies = [
 
 [[package]]
 name = "thiserror"
-version = "1.0.33"
+version = "1.0.37"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3d0a539a918745651435ac7db7a18761589a94cd7e94cd56999f828bf73c8a57"
+checksum = "10deb33631e3c9018b9baf9dcbbc4f737320d2b576bac10f6aefa048fa407e3e"
 dependencies = [
  "thiserror-impl",
 ]
 
 [[package]]
 name = "thiserror-impl"
-version = "1.0.33"
+version = "1.0.37"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c251e90f708e16c49a16f4917dc2131e75222b72edfa9cb7f7c58ae56aae0c09"
+checksum = "982d17546b47146b28f7c22e3d08465f6b8903d0ea13c1660d9d84a6e7adcdbb"
 dependencies = [
  "proc-macro2",
  "quote",
diff --git a/twiq/crates/query_handler/Cargo.toml b/twiq/crates/query_handler/Cargo.toml
index 5021bc9a..67d73537 100644
--- a/twiq/crates/query_handler/Cargo.toml
+++ b/twiq/crates/query_handler/Cargo.toml
@@ -4,4 +4,11 @@ version = "0.0.0"
 edition = "2021"
 
 [dependencies]
+async-trait = "0.1.57"
 domain = { path = "../domain" }
+thiserror = "1.0.37"
+tracing = "0.1.37"
+
+[dev-dependencies]
+anyhow = "1.0.65"
+tokio = { version = "1.21.2", features = ["full"] }
diff --git a/twiq/crates/query_handler/src/in_memory_user_store.rs b/twiq/crates/query_handler/src/in_memory_user_store.rs
new file mode 100644
index 00000000..646bdf22
--- /dev/null
+++ b/twiq/crates/query_handler/src/in_memory_user_store.rs
@@ -0,0 +1,106 @@
+use std::{
+    collections::HashMap,
+    sync::{Arc, Mutex},
+};
+
+use async_trait::async_trait;
+use tracing::instrument;
+
+use crate::{
+    user::User,
+    user_store::{Result, UserStore},
+};
+
+type UserId = String;
+type TwitterUserId = String;
+type TwitterUserName = String;
+
+#[derive(Clone, Debug, Default)]
+pub struct InMemoryUserStore {
+    users: Arc<Mutex<HashMap<UserId, User>>>,
+    twitter_user_ids: Arc<Mutex<HashMap<TwitterUserId, UserId>>>,
+    twitter_user_names: Arc<Mutex<HashMap<TwitterUserName, UserId>>>,
+}
+
+#[async_trait]
+impl UserStore for InMemoryUserStore {
+    #[instrument]
+    async fn find_by_twitter_user_id(
+        &self,
+        twitter_user_id: &TwitterUserId,
+    ) -> Result<Option<User>> {
+        let users = self.users.lock().unwrap();
+        let twitter_user_ids = self.twitter_user_ids.lock().unwrap();
+        Ok(twitter_user_ids
+            .get(twitter_user_id)
+            .and_then(|user_id| users.get(user_id).cloned()))
+    }
+
+    #[instrument]
+    async fn store(&self, before: Option<User>, after: User) -> Result<()> {
+        let mut users = self.users.lock().unwrap();
+        let mut twitter_user_ids = self.twitter_user_ids.lock().unwrap();
+        let mut twitter_user_names = self.twitter_user_names.lock().unwrap();
+
+        match before {
+            None => {}
+            Some(before) => {
+                users.remove(&before.user_id);
+                twitter_user_ids.remove(&before.twitter_user_id);
+                twitter_user_names.remove(&before.twitter_user_name);
+            }
+        }
+
+        let user = users.get_mut(&after.user_id);
+        let twitter_user_id = twitter_user_ids.get_mut(&after.twitter_user_id);
+        let twitter_user_name = twitter_user_names.get_mut(&after.twitter_user_name);
+        match (user, twitter_user_id, twitter_user_name) {
+            (None, None, None) => {
+                users.insert(after.user_id.clone(), after.clone());
+                twitter_user_ids.insert(after.twitter_user_id.clone(), after.user_id.clone());
+                twitter_user_names.insert(after.twitter_user_name.clone(), after.user_id.clone());
+            }
+            _ => unreachable!(),
+        }
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[tokio::test]
+    async fn test() -> anyhow::Result<()> {
+        let user_store = InMemoryUserStore::default();
+        let user1 = User {
+            user_id: "user_id1".to_owned(),
+            twitter_user_id: "twitter_user_id1".to_owned(),
+            twitter_user_name: "twitter_user_name1".to_owned(),
+        };
+        user_store.store(None, user1.clone()).await?;
+        assert!(user_store
+            .find_by_twitter_user_id(&"twitter_user_id2".to_owned())
+            .await?
+            .is_none());
+        assert_eq!(
+            user_store
+                .find_by_twitter_user_id(&"twitter_user_id1".to_owned())
+                .await?,
+            Some(user1.clone())
+        );
+        let user2 = User {
+            user_id: "user_id1".to_owned(),
+            twitter_user_id: "twitter_user_id2".to_owned(),
+            twitter_user_name: "twitter_user_name2".to_owned(),
+        };
+        user_store.store(Some(user1), user2.clone()).await?;
+        assert_eq!(
+            user_store
+                .find_by_twitter_user_id(&"twitter_user_id2".to_owned())
+                .await?,
+            Some(user2)
+        );
+        Ok(())
+    }
+}
diff --git a/twiq/crates/query_handler/src/lib.rs b/twiq/crates/query_handler/src/lib.rs
index 22d12a38..8d55fbe4 100644
--- a/twiq/crates/query_handler/src/lib.rs
+++ b/twiq/crates/query_handler/src/lib.rs
@@ -1 +1,3 @@
+pub mod in_memory_user_store;
 pub mod user;
+pub mod user_store;
diff --git a/twiq/crates/query_handler/src/user.rs b/twiq/crates/query_handler/src/user.rs
index 581a4a72..3e08632a 100644
--- a/twiq/crates/query_handler/src/user.rs
+++ b/twiq/crates/query_handler/src/user.rs
@@ -1,3 +1,4 @@
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct User {
     pub user_id: String,
     pub twitter_user_id: String,
diff --git a/twiq/crates/query_handler/src/user_store.rs b/twiq/crates/query_handler/src/user_store.rs
new file mode 100644
index 00000000..e821016d
--- /dev/null
+++ b/twiq/crates/query_handler/src/user_store.rs
@@ -0,0 +1,23 @@
+use async_trait::async_trait;
+
+use crate::user::User;
+
+#[derive(Debug, Eq, PartialEq, thiserror::Error)]
+pub enum Error {
+    #[error("unknown {0}")]
+    Unknown(String),
+}
+
+pub type Result<T, E = Error> = std::result::Result<T, E>;
+
+#[async_trait]
+pub trait UserStore {
+    async fn find_by_twitter_user_id(&self, twitter_user_id: &String) -> Result<Option<User>>;
+    async fn store(&self, before: Option<User>, after: User) -> Result<()>;
+}
+
+pub trait HasUserStore {
+    type UserStore: UserStore + Send + Sync;
+
+    fn user_store(&self) -> &Self::UserStore;
+}