The Seven Magical Jewels of Ireland is the second book in Robert Adams' series Castaways in Time and returns the reader to a 17th century parallel world wherein the Holy Church has declared a Crusade against the England sovereignty. The sequel picks up not too long after the concluding events of Castaways in Time. The siege of the City of London, the last English bastion of the Catholic papacy, continues. Bass Foster, time traveller from our present, Duke of Norfolk and current Lord Commander of the Royal Horse under King Arthur III, has been soldiering for some time now and would like nothing better than to lay down his arms and settle down with his increasingly discontented wife Krystal and their toddler Joe. The book's opening finds him bemusedly engaged in privateering. Bass is well on his way to starting his own flotilla when he is summoned by the Archbishop Harold of York. Harold is also a time traveller, but from a further future, and he fears his time machine has been re-activated and might imminently bring forth an invading force from his corrupt timeline. Bass must contend with that task, as well as another mission tasked him by King Arthur - to make his way to Ireland and aid in whatever manner Arthur's ally, the beleaguered King Brian.