Frank Cottell Boyce excited about The Return of Colmcille

A giant monster, a patron saint and a massive showdown on the River Foyle - The Return of Colmcille has been billed as one of the highlights of Londonderry's year as the UK City of Culture,

The work is the first piece from Frank Cottrell Boyce since he worked on the opening ceremony of the London Olympic Games.

Around 800 people will take part in the two-day performance.

Derry is the UK City of Culture 2013.

Two weeks ago the city hosted the Radio 1 Big Weekend when acts like Bruno Murs, Olly Murs, the Script and Calvin Harris performed.

Liverpudlian writer Frank Cottrell Boyce was approached to be part of the event when he attended a book signing in Belfast.

"I was given a book about Colmcille and after I read it I just knew I wanted to be involved. It has all the elements of a great story," he said.

"You've got a saint, a journey, the Loch Ness monster, it's a story about revenge. Then you have the river Foyle in Derry and I knew we had to do it on the water. Everything just started to fall into place.

As the performance prepares to get under way, Frank Cottrell Boyce said he was excited about the show opening.

"Derry was founded by Saint Colmcille and he is coming back. He is also the first person to have seen the Loch Ness monster so he is coming back for a massive showdown on the Foyle on Saturday night and between now and Saturday we have a host of smaller, incredibly beautiful and exciting events that include hundreds of people from Derry, monsters, planes, monks and craziness."

The show begins on Friday when a currach (a type of Irish boat) that has travelled from Iona on the western coast of Scotland arrives on the river Foyle with a gift for the city.

The gift will be unveiled on Saturday afternoon in Guildhall Square in the city.

Mr Cottrell Boyce said he was delighted at the number of local people taking part in the water-based spectacle.

"What is brilliant is that it is nearly all performers are from Derry, we have whole families performing together," he said.

"If you walk the walls you will be able to look down and see lots of different performances in the Bogside, Guildhall, by Foyleside.

"It will look as if the whole city has changed. The whole city will become one big performance for Saturday afternoon."

At 21:00 BST on Saturday a siren will sound and people from across the city will be called to the banks of the river Foyle to "protect" the city when it is under attack from a monster.

The performance will cumulate on Saturday evening with a spectacular showdown between Colmcille and the Loch Ness monster on the river.

"Derry is always up for it. What people in the UK don't realise about Derry is that it is a kind of festival city, people are used to getting out and about and being up for things," said Mr Cottrell Boyce.

"I have been quite nervous for the last few days but then last night we had a technical rehearsal and I was walking across the Peace Bridge with my kids after looking at some costumes and suddenly I could hear this terrible roaring and everyone on the bridge stopped and looked round.

"It was us testing the monster's roar. It was still a mile away and you could still induce panic in people.

"There was a really excited atmosphere in the city."