diff --git a/grawlix/output/epub.py b/grawlix/output/epub.py
index a73a23e..4e79dd1 100644
--- a/grawlix/output/epub.py
+++ b/grawlix/output/epub.py
@@ -84,55 +84,91 @@ class Epub(OutputFormat):
 
     async def _download_epub_in_parts(self, data: EpubInParts, metadata: Metadata, location: str, update: Update) -> None:
         files = data.files
-        file_count = len(files)
-        progress = 1/(file_count)
+        progress = 1/len(files)
         temporary_file_location = f"{location}.tmp"
 
-        added_files: set[str] = set()
-        def get_new_files(zipfile: ZipFile):
-            """Returns files in zipfile not already added to file"""
-            for filename in zipfile.namelist():
-                if filename in added_files or filename.endswith(".opf") or filename.endswith(".ncx"):
-                    continue
-                yield filename
+        # First occurrence wins; parts arrive in reading order and share most
+        # files, so insertion order doubles as spine order.
+        collected: dict[str, bytes] = {}
+        try:
+            for file in files:
+                await self._download_and_write_file(file, temporary_file_location)
+                with ZipFile(temporary_file_location, "r") as zipfile:
+                    for filepath in zipfile.namelist():
+                        if filepath.endswith("/") or filepath in collected or self._is_part_packaging(filepath):
+                            continue
+                        collected[filepath] = zipfile.read(filepath)
+                if update:
+                    update(progress)
+        finally:
+            if os.path.exists(temporary_file_location):
+                os.remove(temporary_file_location)
 
+        self._build_epub_from_files(collected, data.files_in_toc, metadata, location)
+
+
+    @staticmethod
+    def _is_part_packaging(filename: str) -> bool:
+        """
+        True for files that belong to a part's own epub packaging. Each part is
+        a complete epub, so copying these into the merged book would leave
+        stray mimetype/container/package files next to the generated ones.
+        """
+        lowered = filename.lower()
+        return (
+            lowered == "mimetype"
+            or lowered.startswith("meta-inf/")
+            or lowered.endswith((".opf", ".ncx"))
+        )
+
+
+    @staticmethod
+    def _build_epub_from_files(
+        files: dict[str, bytes],
+        files_in_toc: dict[str, str],
+        metadata: Metadata,
+        location: str,
+    ) -> None:
+        """
+        Assemble an epub from the raw files collected from its parts. Content
+        documents are stored byte-for-byte as delivered by the source, so their
+        stylesheet links, language attributes and markup survive; only the
+        packaging (opf, ncx, nav) is generated.
+        """
         output = epub.EpubBook()
-        for file in files:
-            await self._download_and_write_file(file, temporary_file_location)
-            with ZipFile(temporary_file_location, "r") as zipfile:
-                for filepath in get_new_files(zipfile):
-                    content = zipfile.read(filepath)
-                    if filepath.endswith("html"):
-                        filename = os.path.basename(filepath)
-                        is_in_toc = False
-                        title = None
-                        for key, value in data.files_in_toc.items():
-                            toc_filename = key.split("#")[0]
-                            if filename == toc_filename:
-                                title = value
-                                is_in_toc = True
-                                break
-                        epub_file = epub.EpubHtml(
-                            title = title,
-                            file_name = filepath,
-                            content = content
-                        )
-                        output.add_item(epub_file)
-                        output.spine.append(epub_file)
-                        if is_in_toc:
-                            output.toc.append(epub_file)
-                    else:
-                        epub_file = epub.EpubItem(
-                            file_name = filepath,
-                            content = content
-                        )
-                        output.add_item(epub_file)
-                    added_files.add(filepath)
-            if update:
-                update(progress)
-        os.remove(temporary_file_location)
+        output.set_title(metadata.title)
+        if metadata.language:
+            output.set_language(metadata.language)
+        for author in metadata.authors:
+            output.add_author(author)
+
+        # Toc keys may or may not carry directory prefixes and fragments
+        # ("Text/chap01.html#nav_1"); compare by basename like the spine files.
+        toc_titles = {
+            os.path.basename(key.split("#")[0]): title
+            for key, title in files_in_toc.items()
+        }
+        cover_flagged = False
+        for filepath, content in files.items():
+            is_content_document = filepath.lower().endswith((".html", ".xhtml", ".htm"))
+            item = epub.EpubItem(
+                file_name = filepath,
+                # Empty media type makes ebooklib guess from the extension
+                media_type = "application/xhtml+xml" if is_content_document else "",
+                content = content,
+            )
+            output.add_item(item)
+            if is_content_document:
+                output.spine.append(item)
+                title = toc_titles.get(os.path.basename(filepath))
+                if title is not None:
+                    output.toc.append(epub.Link(filepath, title, uid=item.get_id()))
+            elif not cover_flagged and os.path.basename(filepath).lower().startswith("cover") \
+                    and item.media_type.startswith("image/"):
+                item.properties = ["cover-image"]
+                output.add_metadata(None, "meta", "", {"name": "cover", "content": item.get_id()})
+                cover_flagged = True
 
         output.add_item(epub.EpubNcx())
         output.add_item(epub.EpubNav())
         epub.write_epub(location, output)
-        exit()