/usr/share/kde4/apps/akonadi/plugins/ is in kdepim-runtime 4:4.8.4-0ubuntu0.2.
This file is owned by root:root, with mode 0o755.
..
/usr/share/kde4/apps/akonadi/plugins/serializer/
/usr/share/kde4/apps/akonadi/plugins/serializer/akonadi_serializer_addressee.desktop
/usr/share/kde4/apps/akonadi/plugins/serializer/akonadi_serializer_bookmark.desktop
/usr/share/kde4/apps/akonadi/plugins/serializer/akonadi_serializer_contactgroup.desktop
/usr/share/kde4/apps/akonadi/plugins/serializer/akonadi_serializer_kalarm.desktop
/usr/share/kde4/apps/akonadi/plugins/serializer/akonadi_serializer_kcal.desktop
/usr/share/kde4/apps/akonadi/plugins/serializer/akonadi_serializer_kcalcore.desktop
/usr/share/kde4/apps/akonadi/plugins/serializer/akonadi_serializer_mail.desktop
/usr/share/kde4/apps/akonadi/plugins/serializer/akonadi_serializer_microblog.desktop