diff --git a/includes/Models/SideConversation.php b/includes/Models/SideConversation.php
new file mode 100644
index 0000000..137861b
--- /dev/null
+++ b/includes/Models/SideConversation.php
@@ -0,0 +1,121 @@
+<?php
+
+namespace Escalated\Models;
+
+use Escalated\Escalated;
+
+/**
+ * A side conversation — a private thread (internal note or outbound email)
+ * attached to a ticket, used by agents to consult colleagues or third
+ * parties without exposing the main customer thread. Mirrors the Laravel
+ * SideConversation model.
+ */
+class SideConversation
+{
+    const CHANNEL_INTERNAL = 'internal';
+
+    const CHANNEL_EMAIL = 'email';
+
+    const STATUS_OPEN = 'open';
+
+    const STATUS_CLOSED = 'closed';
+
+    /**
+     * Get the table name.
+     *
+     * @return string
+     */
+    public static function table()
+    {
+        return Escalated::table('side_conversations');
+    }
+
+    // ---------------------------------------------------------------------
+    // Pure helpers (no database)
+    // ---------------------------------------------------------------------
+
+    /**
+     * Whether a channel value is one of the accepted values.
+     *
+     * @param  string  $channel
+     * @return bool
+     */
+    public static function valid_channel($channel)
+    {
+        return in_array($channel, [self::CHANNEL_INTERNAL, self::CHANNEL_EMAIL], true);
+    }
+
+    // ---------------------------------------------------------------------
+    // Database access
+    // ---------------------------------------------------------------------
+
+    /**
+     * Find a side conversation by ID.
+     *
+     * @param  int  $id
+     * @return object|null
+     */
+    public static function find($id)
+    {
+        global $wpdb;
+        $table = static::table();
+
+        return $wpdb->get_row(
+            $wpdb->prepare("SELECT * FROM {$table} WHERE id = %d", $id)
+        );
+    }
+
+    /**
+     * Create a new side conversation.
+     *
+     * @return int|false Inserted ID or false on failure.
+     */
+    public static function create(array $data)
+    {
+        global $wpdb;
+        $table = static::table();
+        $now = current_time('mysql');
+
+        $data['created_at'] = $now;
+        $data['updated_at'] = $now;
+
+        $result = $wpdb->insert($table, $data);
+
+        return $result !== false ? $wpdb->insert_id : false;
+    }
+
+    /**
+     * Update a side conversation.
+     *
+     * @param  int  $id
+     * @return bool
+     */
+    public static function update($id, array $data)
+    {
+        global $wpdb;
+        $table = static::table();
+
+        $data['updated_at'] = current_time('mysql');
+
+        return $wpdb->update($table, $data, ['id' => $id]) !== false;
+    }
+
+    /**
+     * All side conversations for a ticket, newest first.
+     *
+     * @param  int  $ticket_id
+     * @return array
+     */
+    public static function for_ticket($ticket_id)
+    {
+        global $wpdb;
+        $table = static::table();
+
+        return $wpdb->get_results(
+            $wpdb->prepare(
+                "SELECT * FROM {$table} WHERE ticket_id = %d ORDER BY created_at DESC, id DESC",
+                $ticket_id
+            )
+        ) ?: [];
+    }
+}
diff --git a/includes/Models/SideConversationReply.php b/includes/Models/SideConversationReply.php
new file mode 100644
index 0000000..ad17df9
--- /dev/null
+++ b/includes/Models/SideConversationReply.php
@@ -0,0 +1,60 @@
+<?php
+
+namespace Escalated\Models;
+
+use Escalated\Escalated;
+
+/**
+ * A single message within a SideConversation. Mirrors the Laravel
+ * SideConversationReply model.
+ */
+class SideConversationReply
+{
+    /**
+     * Get the table name.
+     *
+     * @return string
+     */
+    public static function table()
+    {
+        return Escalated::table('side_conversation_replies');
+    }
+
+    /**
+     * Create a new reply.
+     *
+     * @return int|false Inserted ID or false on failure.
+     */
+    public static function create(array $data)
+    {
+        global $wpdb;
+        $table = static::table();
+        $now = current_time('mysql');
+
+        $data['created_at'] = $now;
+        $data['updated_at'] = $now;
+
+        $result = $wpdb->insert($table, $data);
+
+        return $result !== false ? $wpdb->insert_id : false;
+    }
+
+    /**
+     * All replies for a conversation, oldest first.
+     *
+     * @param  int  $side_conversation_id
+     * @return array
+     */
+    public static function for_conversation($side_conversation_id)
+    {
+        global $wpdb;
+        $table = static::table();
+
+        return $wpdb->get_results(
+            $wpdb->prepare(
+                "SELECT * FROM {$table} WHERE side_conversation_id = %d ORDER BY created_at ASC, id ASC",
+                $side_conversation_id
+            )
+        ) ?: [];
+    }
+}
diff --git a/includes/Services/SideConversationService.php b/includes/Services/SideConversationService.php
new file mode 100644
index 0000000..1aff910
--- /dev/null
+++ b/includes/Services/SideConversationService.php
@@ -0,0 +1,108 @@
+<?php
+
+namespace Escalated\Services;
+
+use Escalated\Models\SideConversation;
+use Escalated\Models\SideConversationReply;
+
+/**
+ * Manages side conversations (private internal/email threads on a ticket).
+ * Mirrors the Laravel SideConversationController: creating a conversation
+ * opens it with a first reply, replies can be appended, and a conversation
+ * can be closed.
+ */
+class SideConversationService
+{
+    /**
+     * Open a new side conversation on a ticket with its first reply.
+     *
+     * @param  int  $ticket_id
+     * @param  string  $subject
+     * @param  string  $channel
+     * @param  string  $body
+     * @param  int|string|null  $created_by
+     * @return int|false The new conversation ID, or false on invalid input.
+     */
+    public function create($ticket_id, $subject, $channel, $body, $created_by = null)
+    {
+        $subject = trim((string) $subject);
+        $body = trim((string) $body);
+
+        if ($subject === '' || $body === '' || ! SideConversation::valid_channel($channel)) {
+            return false;
+        }
+
+        $conversation_id = SideConversation::create([
+            'ticket_id' => $ticket_id,
+            'subject' => $subject,
+            'channel' => $channel,
+            'status' => SideConversation::STATUS_OPEN,
+            'created_by' => $created_by,
+        ]);
+
+        if ($conversation_id === false) {
+            return false;
+        }
+
+        SideConversationReply::create([
+            'side_conversation_id' => $conversation_id,
+            'body' => $body,
+            'author_id' => $created_by,
+        ]);
+
+        return $conversation_id;
+    }
+
+    /**
+     * Append a reply to a conversation.
+     *
+     * @param  int  $conversation_id
+     * @param  string  $body
+     * @param  int|string|null  $author_id
+     * @return int|false The new reply ID, or false on invalid input.
+     */
+    public function add_reply($conversation_id, $body, $author_id = null)
+    {
+        $body = trim((string) $body);
+        if ($body === '') {
+            return false;
+        }
+
+        return SideConversationReply::create([
+            'side_conversation_id' => $conversation_id,
+            'body' => $body,
+            'author_id' => $author_id,
+        ]);
+    }
+
+    /**
+     * Close a side conversation.
+     *
+     * @param  int  $conversation_id
+     * @return bool
+     */
+    public function close($conversation_id)
+    {
+        return SideConversation::update($conversation_id, [
+            'status' => SideConversation::STATUS_CLOSED,
+        ]);
+    }
+
+    /**
+     * All side conversations for a ticket (newest first), each with its
+     * replies attached as a `replies` property.
+     *
+     * @param  int  $ticket_id
+     * @return array
+     */
+    public function for_ticket($ticket_id)
+    {
+        $conversations = SideConversation::for_ticket($ticket_id);
+
+        foreach ($conversations as $conversation) {
+            $conversation->replies = SideConversationReply::for_conversation($conversation->id);
+        }
+
+        return $conversations;
+    }
+}
diff --git a/includes/class-activator.php b/includes/class-activator.php
index 70188c9..367cec0 100644
--- a/includes/class-activator.php
+++ b/includes/class-activator.php
@@ -599,6 +599,34 @@ private static function create_tables(): void
             UNIQUE KEY user_channel (user_id, channel)
         ) $charset_collate;";
         dbDelta($sql);
+
+        // 32. escalated_side_conversations
+        $sql = "CREATE TABLE {$prefix}side_conversations (
+            id BIGINT UNSIGNED NOT NULL AUTO_INCREMENT,
+            ticket_id BIGINT UNSIGNED NOT NULL,
+            subject VARCHAR(255) NOT NULL,
+            channel VARCHAR(32) NOT NULL,
+            status VARCHAR(32) NOT NULL,
+            created_by BIGINT UNSIGNED NULL,
+            created_at DATETIME,
+            updated_at DATETIME,
+            PRIMARY KEY  (id),
+            KEY ticket_id (ticket_id)
+        ) $charset_collate;";
+        dbDelta($sql);
+
+        // 33. escalated_side_conversation_replies
+        $sql = "CREATE TABLE {$prefix}side_conversation_replies (
+            id BIGINT UNSIGNED NOT NULL AUTO_INCREMENT,
+            side_conversation_id BIGINT UNSIGNED NOT NULL,
+            body LONGTEXT NOT NULL,
+            author_id BIGINT UNSIGNED NULL,
+            created_at DATETIME,
+            updated_at DATETIME,
+            PRIMARY KEY  (id),
+            KEY side_conversation_id (side_conversation_id)
+        ) $charset_collate;";
+        dbDelta($sql);
     }
 
     /**
diff --git a/tests/Test_Side_Conversation_Service.php b/tests/Test_Side_Conversation_Service.php
new file mode 100644
index 0000000..75aef67
--- /dev/null
+++ b/tests/Test_Side_Conversation_Service.php
@@ -0,0 +1,85 @@
+<?php
+
+/**
+ * Tests for side conversations.
+ *
+ * Pure-function test for valid_channel; the create / reply / close flow is
+ * exercised via a live wpdb (the test suite's mysql harness).
+ */
+
+use Escalated\Models\SideConversation;
+use Escalated\Models\SideConversationReply;
+use Escalated\Services\SideConversationService;
+
+class Test_Side_Conversation_Service extends WP_UnitTestCase
+{
+    // ---------------------------------------------------------------------
+    // valid_channel (pure)
+    // ---------------------------------------------------------------------
+
+    public function test_valid_channel()
+    {
+        $this->assertTrue(SideConversation::valid_channel('internal'));
+        $this->assertTrue(SideConversation::valid_channel('email'));
+        $this->assertFalse(SideConversation::valid_channel('sms'));
+        $this->assertFalse(SideConversation::valid_channel(''));
+    }
+
+    // ---------------------------------------------------------------------
+    // Service flow (live wpdb)
+    // ---------------------------------------------------------------------
+
+    public function test_create_opens_conversation_with_first_reply()
+    {
+        $service = new SideConversationService;
+
+        $id = $service->create(555, 'Need vendor input', 'internal', 'Can you advise?', 7);
+        $this->assertNotFalse($id);
+
+        $conversation = SideConversation::find($id);
+        $this->assertEquals('open', $conversation->status);
+        $this->assertEquals('Need vendor input', $conversation->subject);
+
+        $replies = SideConversationReply::for_conversation($id);
+        $this->assertCount(1, $replies);
+        $this->assertEquals('Can you advise?', $replies[0]->body);
+    }
+
+    public function test_create_rejects_invalid_input()
+    {
+        $service = new SideConversationService;
+
+        $this->assertFalse($service->create(555, '', 'internal', 'body'));
+        $this->assertFalse($service->create(555, 'Subject', 'sms', 'body'));
+        $this->assertFalse($service->create(555, 'Subject', 'internal', '   '));
+    }
+
+    public function test_add_reply_and_close()
+    {
+        $service = new SideConversationService;
+
+        $id = $service->create(556, 'Thread', 'email', 'First', 7);
+        $this->assertNotFalse($service->add_reply($id, 'Second', 9));
+        $this->assertFalse($service->add_reply($id, '   '));
+
+        $replies = SideConversationReply::for_conversation($id);
+        $this->assertCount(2, $replies);
+
+        $service->close($id);
+        $this->assertEquals('closed', SideConversation::find($id)->status);
+    }
+
+    public function test_for_ticket_attaches_replies_newest_first()
+    {
+        $service = new SideConversationService;
+
+        $service->create(557, 'Older', 'internal', 'a', 7);
+        $newer = $service->create(557, 'Newer', 'internal', 'b', 7);
+        $service->add_reply($newer, 'b2', 7);
+
+        $threads = $service->for_ticket(557);
+        $this->assertCount(2, $threads);
+        $this->assertEquals('Newer', $threads[0]->subject);
+        $this->assertCount(2, $threads[0]->replies);
+    }
+}