The Avengers #115

"Below Us the Battle!" 

Traveling to England to search for their missing comrade, the Black Knight, the Avengers are stopped by the British division of SHIELD because they are carrying the Swordsman and Mantis aboard their Quinjet. Explaining that the Swordsman has reformed, they decide to grant him temporary amnesty while in Britain.  Arriving at the Black Knight's castle, they find that it's protected by an invisible barrier. Their presence near the castle alerts the attention of Skol and his army of Troglodytes, a group of underground dwellers who were forced into living under the castle for centuries.

"Prologue: Alliance Most Foul!"

 Blinded and defeated by Thor (in Thor #207) Loki plunged himself off a cliff to escape battle, however, before he could ever hit the bottom he is suddenly transported away. He finds himself transported to the Dark Dimension by Dormammu.