diff --git a/src/files.cpp b/src/files.cpp
index a937dd2..5f4c36e 100644
--- a/src/files.cpp
+++ b/src/files.cpp
@@ -17,6 +17,7 @@
 #include "files.hpp"
 
 #include "fs-compat.hpp"
+#include "log.hpp"
 
 #include <exception>
 #include <string_view>
@@ -42,6 +43,7 @@ std::vector<fs::path> list_recursive(const fs::path &directory,
         if (!path.is_directory())
         {
             paths.emplace_back(path);
+            DEBUGLOG << "Added file: " << path;
         }
     }
 
diff --git a/src/main.cpp b/src/main.cpp
index a339f7f..b9f6cf1 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -84,6 +84,7 @@ int main(int argc, char *argv[])
     {
         log::enable_debug();
     }
+    DEBUGLOG << "Options: " << opts;
 
     if (opts.help || opts.version)
     {
@@ -97,8 +98,8 @@ int main(int argc, char *argv[])
     {
         if (!opts.recursive && !opts.dereference_recursive)
         {
-
             input_files.emplace_back(filepath);
+            DEBUGLOG << "Added to input_files: " << filepath;
         }
         else
         {
@@ -109,12 +110,14 @@ int main(int argc, char *argv[])
                                           opts.dereference_recursive)};
                 input_files.insert(input_files.end(), files_in_dir.begin(),
                                    files_in_dir.end());
+                DEBUGLOG << "Added directory to input_files.";
             }
             catch (const fs::filesystem_error &e)
             {
                 if (e.code().value() == 20)
                 { // Is not a directory.
                     input_files.emplace_back(filepath);
+                    DEBUGLOG << "Added to input_files: " << filepath;
                     continue;
                 }
 
@@ -203,15 +206,18 @@ int main(int argc, char *argv[])
             auto n{static_cast<double>(std::thread::hardware_concurrency())};
             return static_cast<std::uint32_t>(std::ceil(n / 2 + n / 4));
         }()};
+    DEBUGLOG << "max_threads = " << max_threads;
 
     for (const auto &filepath : input_files)
     {
         while (futurepool.size() >= max_threads)
         {
+            DEBUGLOG << "Attempting to clean up threads";
             futures_cleanup();
         }
         futurepool.emplace_back(
             std::async(std::launch::async, search_file, filepath));
+        DEBUGLOG << "Launched new thread";
 
         if (!matches_all.empty())
         {
@@ -221,6 +227,7 @@ int main(int argc, char *argv[])
             matches_all.erase(matches_all.begin());
         }
     }
+    DEBUGLOG << "Waiting for remaining threads to finish";
     futures_cleanup(true);
 
     for (const auto &matches : matches_all)
diff --git a/src/search.cpp b/src/search.cpp
index 1be5c92..91bf4ae 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -18,9 +18,12 @@
 
 #include "fs-compat.hpp"
 #include "helpers.hpp"
+#include "log.hpp"
 #include "zip.hpp"
 
 #include <boost/regex.hpp>
+#include <fmt/format.h>
+#include <fmt/ostream.h> // For compatibility with fmt 4.
 
 #include <algorithm>
 #include <array>
@@ -31,11 +34,14 @@
 namespace epubgrep::search
 {
 
+using fmt::format;
 using std::string;
 
 std::vector<match> search(const fs::path &filepath,
                           const std::string_view regex, const settings &opts)
 {
+    DEBUGLOG << format(R"(Starting search in {0:s} using regex "{1:s}")",
+                       filepath, regex);
     boost::regex::flag_type flags{};
 
     switch (opts.regex)
@@ -75,6 +81,7 @@ std::vector<match> search(const fs::path &filepath,
 
     for (const auto &entry : epub_filepaths)
     {
+        DEBUGLOG << "Processing " << entry;
         auto document{zip::read_file(filepath, entry)};
         if (!opts.raw)
         {
diff --git a/src/zip.cpp b/src/zip.cpp
index 4e9153a..a8cd40a 100644
--- a/src/zip.cpp
+++ b/src/zip.cpp
@@ -61,6 +61,7 @@ std::vector<std::string> list(const fs::path &filepath)
             continue;
         }
         toc.emplace_back(in_epub_filepath);
+        DEBUGLOG << "Found in file: " << in_epub_filepath;
         archive_read_data_skip(zipfile);
     }
 
@@ -189,6 +190,7 @@ std::vector<std::string> list_spine(const fs::path &filepath)
     std::vector<std::string> spine_filepaths;
     if (!opf_file_path.empty())
     {
+        DEBUGLOG << "Parsing " << opf_file_path;
         pugi::xml_document xml;
         const std::string opf_file{read_file(filepath, opf_file_path.string())};
         const auto result{xml.load_buffer(&opf_file[0], opf_file.size())};
@@ -209,15 +211,20 @@ std::vector<std::string> list_spine(const fs::path &filepath)
             {
                 const auto &idref{itemref.attribute("idref").value()};
                 const auto &item{manifest.find_child_by_attribute("id", idref)};
-                const std::string href{
+                const auto href{
                     helpers::urldecode(item.attribute("href").value())};
-                if (href[0] != '/')
-                {
-                    spine_filepaths.emplace_back(
-                        opf_file_path.parent_path() /= href);
-                    continue;
-                }
-                spine_filepaths.emplace_back(href);
+                const auto real_href{
+                    [&href, &spine_filepaths, &opf_file_path]
+                    {
+                        if (href[0] != '/')
+                        {
+                            return spine_filepaths.emplace_back(
+                                opf_file_path.parent_path() /= href);
+                        }
+                        return href;
+                    }()};
+                DEBUGLOG << "Found in spine: " << real_href;
+                spine_filepaths.emplace_back(real_href);
             }
         }
         else