diff --git a/src/calibre/gui2/viewer2/convert_book.py b/src/calibre/gui2/viewer2/convert_book.py
new file mode 100644
index 0000000000..aa34ca6d64
--- /dev/null
+++ b/src/calibre/gui2/viewer2/convert_book.py
@@ -0,0 +1,150 @@
+#!/usr/bin/env python2
+# vim:fileencoding=utf-8
+# License: GPL v3 Copyright: 2018, Kovid Goyal <kovid at kovidgoyal.net>
+
+from __future__ import absolute_import, division, print_function, unicode_literals
+
+import errno
+import json
+import os
+import shutil
+import tempfile
+import time
+from cPickle import dumps
+from hashlib import sha1
+
+from calibre import walk
+from calibre.constants import cache_dir
+from calibre.srv.render_book import RENDER_VERSION
+from calibre.utils.ipc.simple_worker import fork_job
+from calibre.utils.lock import ExclusiveFile
+
+DAY = 24 * 3600
+
+
+def book_cache_dir():
+    return os.path.join(cache_dir(), 'ev2')
+
+
+def cache_lock():
+    return ExclusiveFile(os.path.join(book_cache_dir(), 'metadata.json'))
+
+
+def book_hash(path, size, mtime):
+    path = os.path.normcase(os.path.abspath(path))
+    raw = dumps((path, size, mtime, RENDER_VERSION))
+    return sha1(raw).hexdigest().decode('ascii')
+
+
+def safe_makedirs(path):
+    try:
+        os.makedirs(path)
+    except EnvironmentError as err:
+        if err.errno != errno.EEXIST:
+            raise
+
+
+def clear_temp(temp_path):
+    now = time.time()
+    for x in os.listdir(temp_path):
+        x = os.path.join(temp_path, x)
+        st = os.stat(x)
+        if now - st.st_mtime > DAY:
+            try:
+                shutil.rmtree(x)
+            except EnvironmentError:
+                pass
+
+
+def expire_cache(path, instances):
+    now = time.time()
+    remove = [x for x in instances if now - instances['atime'] > 30 * DAY]
+    for instance in remove:
+        instances.remove(instance)
+        if instances['status'] == 'finished':
+            try:
+                shutil.rmtree(os.path.join(path, instances['path']))
+            except Exception:
+                pass
+
+
+def expire_cache_and_temp(temp_path, finished_path, metadata):
+    now = time.time()
+    if now - metadata['last_clear_at'] < DAY:
+        return
+    clear_temp(temp_path)
+    entries = metadata['entries']
+    for key, instances in tuple(entries.items()):
+        expire_cache(finished_path, instances)
+        if not instances:
+            del entries[key]
+    metadata['last_clear_at'] = now
+
+
+def prepare_convert(temp_path, key, st):
+    tdir = tempfile.mkdtemp(dir=temp_path)
+    now = time.time()
+    return {
+        'path': os.path.basename(tdir),
+        'status': 'working',
+        'mtime': now,
+        'atime': now,
+        'key': key,
+        'file_mtime': st.st_mtime,
+        'file_size': st.st_size,
+        'cache_size': 0,
+    }
+
+
+def do_convert(path, temp_path, key, instance):
+    tdir = os.path.join(temp_path, instance['path'])
+    fork_job('calibre.srv.render_book', 'render', args=(
+        path, tdir, {'size': instance['file_size'], 'mtime': instance['file_mtime'], 'hash': key}
+        ), timeout=3000, no_output=True
+    )
+    size = 0
+    for f in walk(tdir):
+        size += os.path.getsize(f)
+    instance['cache_size'] = size
+
+
+def prepare_book(path):
+    st = os.stat(path)
+    key = book_hash(path, st.st_size, st.st_mtime)
+    finished_path = safe_makedirs(os.path.join(book_cache_dir(), 'f'))
+    temp_path = safe_makedirs(os.path.join(book_cache_dir(), 't'))
+    with cache_lock() as f:
+        try:
+            metadata = json.loads(f.read())
+        except ValueError:
+            metadata = {'entries': [], 'last_clear_at': 0}
+        entries = metadata['entries']
+        instances = entries.setdefault(key, [])
+        for instance in instances:
+            if instance['status'] == 'finished':
+                instance['atime'] = time.time()
+                f.seek(0), f.write(json.dumps(metadata))
+                return os.path.join(finished_path, instance['path'])
+        instance = prepare_convert(temp_path, key, st)
+        instances.append(instance)
+        f.seek(0), f.write(json.dumps(metadata))
+    do_convert(path, temp_path, key, instance)
+    src_path = os.path.join(temp_path, instance['path'])
+    with cache_lock() as f:
+        ans = tempfile.mkdtemp(dir=finished_path)
+        instance['path'] = os.path.basename(ans)
+        try:
+            metadata = json.loads(f.read())
+        except ValueError:
+            metadata = {'entries': [], 'last_cleat_at': 0}
+        entries = metadata['entries']
+        instances = entries.setdefault(key, [])
+        os.rmdir(ans)
+        os.rename(src_path, ans)
+        for q in instances:
+            if q['id'] == instance['id']:
+                q.update(instance)
+                break
+        expire_cache_and_temp(temp_path, finished_path, metadata)
+        f.seek(0), f.write(json.dumps(metadata))
+    return ans