diff --git a/.eslintrc.js b/.eslintrc.js
index 6e3ee44b1..8a6120396 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -14,5 +14,13 @@ module.exports = {
   },
   rules: {
     'prettier/prettier': 'error'
-  }
+  },
+  overrides: [
+    {
+      files: ['config/webpack/*.js'],
+      env: {
+        node: true
+      }
+    }
+  ]
 };
diff --git a/app/assets/stylesheets/new_design/dossier_show.scss b/app/assets/stylesheets/new_design/dossier_show.scss
index def3e15d3..be12db19e 100644
--- a/app/assets/stylesheets/new_design/dossier_show.scss
+++ b/app/assets/stylesheets/new_design/dossier_show.scss
@@ -38,4 +38,15 @@
   .messagerie-explanation {
     margin-bottom: $default-padding * 2;
   }
+
+  .latest-message-section {
+    display: flex;
+    flex-direction: column;
+    max-width: 700px;
+    margin-bottom: $default-padding * 2;
+
+    .button.send {
+      align-self: flex-end;
+    }
+  }
 }
diff --git a/app/assets/stylesheets/new_design/message.scss b/app/assets/stylesheets/new_design/message.scss
index 025a7783e..7c87e763e 100644
--- a/app/assets/stylesheets/new_design/message.scss
+++ b/app/assets/stylesheets/new_design/message.scss
@@ -9,6 +9,10 @@
   background: #FFFFFF;
   border-radius: 3px;
 
+  &.inverted-background {
+    background: $light-grey;
+  }
+
   .person-icon {
     margin-right: $default-spacer;
   }
diff --git a/app/assets/stylesheets/new_design/status_overview.scss b/app/assets/stylesheets/new_design/status_overview.scss
index 49ad8a55b..55643b1d3 100644
--- a/app/assets/stylesheets/new_design/status_overview.scss
+++ b/app/assets/stylesheets/new_design/status_overview.scss
@@ -3,6 +3,7 @@
 
 .status-overview {
   text-align: center;
+  margin-bottom: $default-padding * 2;
 }
 
 .status-timeline {
diff --git a/app/helpers/commentaire_helper.rb b/app/helpers/commentaire_helper.rb
index f22163a07..f42450024 100644
--- a/app/helpers/commentaire_helper.rb
+++ b/app/helpers/commentaire_helper.rb
@@ -1,10 +1,18 @@
 module CommentaireHelper
-  def commentaire_is_from_me_class(commentaire, email)
-    if commentaire.email == email
+  def commentaire_is_from_me_class(commentaire, connected_user)
+    if commentaire_is_from_me(commentaire, connected_user)
       "from-me"
     end
   end
 
+  def commentaire_answer_action(commentaire, connected_user)
+    if commentaire_is_from_me(commentaire, connected_user)
+      "Envoyer un message à l’instructeur"
+    else
+      "Répondre dans la messagerie"
+    end
+  end
+
   def commentaire_is_from_guest(commentaire)
     commentaire.dossier.invites.map(&:email).include?(commentaire.email)
   end
@@ -14,4 +22,10 @@ module CommentaireHelper
     template = is_current_year ? :message_date : :message_date_with_year
     I18n.l(commentaire.created_at.localtime, format: template)
   end
+
+  private
+
+  def commentaire_is_from_me(commentaire, connected_user)
+    commentaire.email == connected_user.email
+  end
 end
diff --git a/app/javascript/packs/application-old.js b/app/javascript/packs/application-old.js
index 44fa321c8..214d87b4e 100644
--- a/app/javascript/packs/application-old.js
+++ b/app/javascript/packs/application-old.js
@@ -1,13 +1,9 @@
+import '../shared/polyfills';
 import Turbolinks from 'turbolinks';
 import Rails from 'rails-ujs';
 import ActiveStorage from '../shared/activestorage/ujs';
 import jQuery from 'jquery';
 
-// Include runtime-polyfills for older browsers.
-// Due to .babelrc's 'useBuiltIns', only polyfills actually
-// required by the browsers we support will be included.
-import 'babel-polyfill';
-
 import '../shared/sentry';
 import '../shared/rails-ujs-fix';
 import '../shared/safari-11-file-xhr-workaround';
diff --git a/app/javascript/packs/application.js b/app/javascript/packs/application.js
index 971840e3a..196074a15 100644
--- a/app/javascript/packs/application.js
+++ b/app/javascript/packs/application.js
@@ -1,3 +1,4 @@
+import '../shared/polyfills';
 import Turbolinks from 'turbolinks';
 import Rails from 'rails-ujs';
 import ActiveStorage from '../shared/activestorage/ujs';
@@ -5,11 +6,6 @@ import Chartkick from 'chartkick';
 import Highcharts from 'highcharts';
 import jQuery from 'jquery';
 
-// Include runtime-polyfills for older browsers.
-// Due to .babelrc's 'useBuiltIns', only polyfills actually
-// required by the browsers we support will be included.
-import 'babel-polyfill';
-
 import '../shared/sentry';
 import '../shared/rails-ujs-fix';
 import '../shared/safari-11-file-xhr-workaround';
diff --git a/app/javascript/shared/polyfills.js b/app/javascript/shared/polyfills.js
new file mode 100644
index 000000000..09b38e23e
--- /dev/null
+++ b/app/javascript/shared/polyfills.js
@@ -0,0 +1,5 @@
+// Include runtime-polyfills for older browsers.
+// Due to .babelrc's 'useBuiltIns', only polyfills actually
+// required by the browsers we support will be included.
+import 'babel-polyfill';
+import 'dom4';
diff --git a/app/views/new_user/dossiers/show.html.haml b/app/views/new_user/dossiers/show.html.haml
index e6e17707c..b94a0686f 100644
--- a/app/views/new_user/dossiers/show.html.haml
+++ b/app/views/new_user/dossiers/show.html.haml
@@ -5,3 +5,13 @@
 
   .container
     = render partial: 'new_user/dossiers/show/status_overview', locals: { dossier: @dossier }
+
+    - latest_message = @dossier.commentaires.last
+    - if latest_message.present?
+      .latest-message-section
+        %h3.tab-title Dernier message
+
+        .message.inverted-background
+          = render partial: "shared/dossiers/messages/message", locals: { commentaire: latest_message, connected_user: current_user, messagerie_seen_at: nil }
+
+        = link_to commentaire_answer_action(latest_message, current_user), messagerie_dossier_url(@dossier, anchor: 'new_commentaire'), class: 'button send'
diff --git a/app/views/shared/dossiers/_messagerie.html.haml b/app/views/shared/dossiers/_messagerie.html.haml
index c67d4a174..5d589fa5b 100644
--- a/app/views/shared/dossiers/_messagerie.html.haml
+++ b/app/views/shared/dossiers/_messagerie.html.haml
@@ -1,7 +1,7 @@
 .messagerie.container
   %ul.messages-list
     - dossier.commentaires.each do |commentaire|
-      %li.message{ class: commentaire_is_from_me_class(commentaire, connected_user.email) }
+      %li.message{ class: commentaire_is_from_me_class(commentaire, connected_user) }
         = render partial: "shared/dossiers/messages/message", locals: { commentaire: commentaire, connected_user: connected_user, messagerie_seen_at: messagerie_seen_at }
 
   = render partial: "shared/dossiers/messages/form", locals: { commentaire: new_commentaire, form_url: form_url }
diff --git a/config/webpack/development.js b/config/webpack/development.js
index c5edff94a..89d35d938 100644
--- a/config/webpack/development.js
+++ b/config/webpack/development.js
@@ -1,5 +1,5 @@
-process.env.NODE_ENV = process.env.NODE_ENV || 'development'
+process.env.NODE_ENV = process.env.NODE_ENV || 'development';
 
-const environment = require('./environment')
+const environment = require('./environment');
 
-module.exports = environment.toWebpackConfig()
+module.exports = environment.toWebpackConfig();
diff --git a/config/webpack/environment.js b/config/webpack/environment.js
index b4f720be3..d261e8336 100644
--- a/config/webpack/environment.js
+++ b/config/webpack/environment.js
@@ -1,4 +1,4 @@
-const { environment } = require('@rails/webpacker')
+const { environment } = require('@rails/webpacker');
 
 // By default don't transpile JS files in ./node_modules – except for some specific modules.
 const babelLoader = environment.loaders.get('babel');
@@ -6,8 +6,12 @@ babelLoader.exclude = function(modulePath) {
   let forcedModules = [
     'activestorage' // ActiveStorage uses 'class', which is not supported by IE 11 and older Safari version
   ];
-  return modulePath.includes('node_modules')
-    && forcedModules.every(forcedModule => !modulePath.includes('node_modules/' + forcedModule));
-}
+  return (
+    modulePath.includes('node_modules') &&
+    forcedModules.every(
+      forcedModule => !modulePath.includes('node_modules/' + forcedModule)
+    )
+  );
+};
 
-module.exports = environment
+module.exports = environment;
diff --git a/config/webpack/production.js b/config/webpack/production.js
index 067efd4e4..0103278ee 100644
--- a/config/webpack/production.js
+++ b/config/webpack/production.js
@@ -1,9 +1,9 @@
-process.env.NODE_ENV = process.env.NODE_ENV || 'production'
+process.env.NODE_ENV = process.env.NODE_ENV || 'production';
 
-const environment = require('./environment')
+const environment = require('./environment');
 
 // https://github.com/rails/webpacker/issues/1235
 environment.config.optimization.minimizer[0].options.uglifyOptions.ecma = 5; // for IE 11 support
 environment.config.optimization.minimizer[0].options.uglifyOptions.safari10 = true;
 
-module.exports = environment.toWebpackConfig()
+module.exports = environment.toWebpackConfig();
diff --git a/config/webpack/test.js b/config/webpack/test.js
index c5edff94a..89d35d938 100644
--- a/config/webpack/test.js
+++ b/config/webpack/test.js
@@ -1,5 +1,5 @@
-process.env.NODE_ENV = process.env.NODE_ENV || 'development'
+process.env.NODE_ENV = process.env.NODE_ENV || 'development';
 
-const environment = require('./environment')
+const environment = require('./environment');
 
-module.exports = environment.toWebpackConfig()
+module.exports = environment.toWebpackConfig();
diff --git a/package.json b/package.json
index b68dcd7ed..d40a59cc6 100644
--- a/package.json
+++ b/package.json
@@ -6,6 +6,7 @@
     "autocomplete.js": "^0.31.0",
     "chartkick": "^2.3.6",
     "debounce": "^1.2.0",
+    "dom4": "^2.1.3",
     "highcharts": "^6.1.1",
     "jquery": "^3.3.1",
     "leaflet": "^1.3.1",
@@ -21,7 +22,7 @@
     "webpack-dev-server": "^3.1.4"
   },
   "scripts": {
-    "lint:js": "eslint ./app/javascript"
+    "lint:js": "eslint ./app/javascript ./config/webpack"
   },
   "engines": {
     "node": "6.* || 8.* || >= 10.*"
diff --git a/spec/features/new_user/dossier_details_spec.rb b/spec/features/new_user/dossier_details_spec.rb
index d6644e634..41575988b 100644
--- a/spec/features/new_user/dossier_details_spec.rb
+++ b/spec/features/new_user/dossier_details_spec.rb
@@ -4,7 +4,7 @@ describe 'Dossier details:' do
     tdcs = [create(:type_de_champ, libelle: 'texte obligatoire')]
     create(:procedure, :published, :for_individual, types_de_champ: tdcs)
   end
-  let(:dossier) { create(:dossier, :en_construction, :for_individual, user: user, procedure: simple_procedure) }
+  let(:dossier) { create(:dossier, :en_construction, :for_individual, :with_commentaires, user: user, procedure: simple_procedure) }
 
   before do
     Flipflop::FeatureSet.current.test!.switch!(:new_dossier_details, true)
@@ -16,6 +16,7 @@ describe 'Dossier details:' do
     expect(page).to have_current_path(dossier_path(dossier))
     expect(page).to have_content(dossier.id)
     expect(page).to have_selector('.status-explanation')
+    expect(page).to have_text(dossier.commentaires.last.body)
   end
 
   scenario 'the user can see and edit dossier before instruction' do
diff --git a/spec/helpers/commentaire_helper_spec.rb b/spec/helpers/commentaire_helper_spec.rb
index 9f0bd998b..36d235f42 100644
--- a/spec/helpers/commentaire_helper_spec.rb
+++ b/spec/helpers/commentaire_helper_spec.rb
@@ -1,24 +1,36 @@
 require 'rails_helper'
 
 RSpec.describe CommentaireHelper, type: :helper do
-  describe ".commentaire_is_from_me_class" do
-    let(:commentaire) { create(:commentaire, email: "michel@pref.fr") }
+  let(:commentaire) { create(:commentaire, email: "michel@pref.fr") }
 
+  describe ".commentaire_is_from_me_class" do
     subject { commentaire_is_from_me_class(commentaire, me) }
 
     context "when commentaire is from me" do
-      let(:me) { "michel@pref.fr" }
-
+      let(:me) { User.new(email: "michel@pref.fr") }
       it { is_expected.to eq("from-me") }
     end
 
     context "when commentaire is not from me" do
-      let(:me) { "roger@usager.fr" }
-
+      let(:me) { User.new(email: "roger@usager.fr") }
       it { is_expected.to eq nil }
     end
   end
 
+  describe '.commentaire_answer_action' do
+    subject { commentaire_answer_action(commentaire, me) }
+
+    context "when commentaire is from me" do
+      let(:me) { User.new(email: "michel@pref.fr") }
+      it { is_expected.to include('Envoyer') }
+    end
+
+    context "when commentaire is not from me" do
+      let(:me) { User.new(email: "roger@usager.fr") }
+      it { is_expected.to include('Répondre') }
+    end
+  end
+
   describe '.commentaire_is_from_guest' do
     let(:dossier) { create(:dossier) }
     let!(:guest) { create(:invite_user, dossier: dossier) }
diff --git a/spec/views/new_user/dossiers/show.html.haml_spec.rb b/spec/views/new_user/dossiers/show.html.haml_spec.rb
index 303f1f244..977b5677b 100644
--- a/spec/views/new_user/dossiers/show.html.haml_spec.rb
+++ b/spec/views/new_user/dossiers/show.html.haml_spec.rb
@@ -1,7 +1,7 @@
 require 'spec_helper'
 
 describe 'new_user/dossiers/show.html.haml', type: :view do
-  let(:dossier) { create(:dossier, :en_construction, procedure: create(:procedure)) }
+  let(:dossier) { create(:dossier, :en_construction) }
 
   before do
     sign_in dossier.user
@@ -14,4 +14,15 @@ describe 'new_user/dossiers/show.html.haml', type: :view do
     expect(rendered).to have_text("Dossier nº #{dossier.id}")
     expect(rendered).to have_selector('.status-overview')
   end
+
+  context 'with messages' do
+    let(:first_message) { create(:commentaire, body: 'Premier message') }
+    let(:last_message)  { create(:commentaire, body: 'Second message') }
+    let(:dossier) { create(:dossier, :en_construction, commentaires: [first_message, last_message]) }
+
+    it 'displays the last message' do
+      expect(rendered).not_to have_text(first_message.body)
+      expect(rendered).to have_text(last_message.body)
+    end
+  end
 end
diff --git a/yarn.lock b/yarn.lock
index 72a33df3d..2921fab46 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -2319,6 +2319,10 @@ doctrine@^2.1.0:
   dependencies:
     esutils "^2.0.2"
 
+dom4@^2.1.3:
+  version "2.1.3"
+  resolved "https://registry.yarnpkg.com/dom4/-/dom4-2.1.3.tgz#f71808fe1f141e4da4ebc43ad5ddb3dd521f2767"
+
 domain-browser@^1.1.1:
   version "1.2.0"
   resolved "https://registry.yarnpkg.com/domain-browser/-/domain-browser-1.2.0.tgz#3d31f50191a6749dd1375a7f522e823d42e54eda"