Workmen are raising the walls around the Assemblies of God Church on the outskirts of Zanzibar's Stone Town, cementing row after row of concrete blocks to a height of some 10ft. Earlier this year a mob stormed this compound and burned the church inside. Six months on from the attack, licks of black smoke still darken the cross on its walls. Bishop Dickson Kaganga, who now has bars on the window of his office, says he and his fellow Christians are "living in fear" of a repeat. The Pentecostal priest, whose car was also torched in the May assault, talks darkly of a rising tide of radicalism on the Indian Ocean archipelago once famed for its cosmopolitanism and religious tolerance.
After 16 years work as a missionary on the overwhelmingly Muslim archipelago, the bishop has little doubt who is to blame for the attacks that ruined his church and ransacked several others. He points to the rise of a group calling itself "The Awakening", or "Uamsho" in the islands' native Swahili. A religious charity which historically confined itself to propagating Islam but has recently entered the political realm with its own brand of faith-based populism, the group's loud calls for independence from Tanzania and anti-mainlander rhetoric have proven hugely popular. Mr Kaganga insists that they are "advocating chaos".
The church burnings coincided with the arrest of Uamsho's leader, the cleric Farid Hadi Ahmed, in connection with an illegal demonstration. The following day witnessed some of the worst riots seen on Zanzibar.
The leadership of the group has denied any involvement in the attacks and no arrests have been made. Since then a pattern of arrests, riots and unrest has dogged the islands, culminating in the deaths of several protesters and one policeman earlier this month. With its population of one million people split between the two main islands of Unguja and Pemba, Zanzibar is no stranger to political violence. Shortly after independence from Britain in 1963 the black African islanders, many descended from slaves traded through the archipelago, overthrew the Arab Sultan.
A year later its new leaders declared union with mainland Tanganyika – creating Tanzania. The islands' history as an African entry point for Christian missionaries, a transit centre for the slave trade and a hub for Islamic scholars have all left their mark.
Little of this rich, turbulent history sits comfortably with Zanzibar's modern fame as a tropical tourist destination with a spiced history of cloves and slaves. Beyond the glamorously dilapidated streets of Stone Town and sun loungers of the beachfront hotels, more than one-third of the population lives in grinding poverty. The large underclass, living in rural villages or the crumbling concrete apartment blocks built by Soviet-era allies in the 1960s, face problems which don't appear in holiday brochures. Dadi Kombo Maalim, the chairperson of Zanzibar's youth forum, says that unemployment among under-30s could be running as high as 80 per cent. Heroin addiction has been rising slowly since the 1980s and has now reached epidemic proportions. The popular scapegoat for all the islands' ills has been half-century of union with the mainland, which is blamed for both the economic doldrums and the perceived creeping moral decay.
"Uamsho says that in the name of the union many corrupt things have been brought from the mainland," says Mr Maalim, who lists prostitution, drugs, theft and alcohol. It has left many Zanzibaris feeling that Uamsho "speaks for them", he says.
There are few obvious trappings of wealth at a meeting of Uamsho's leaders in a poorly-lit spice shop on the rougher side of the island's capital, Ng'ambo, which literally means the "other side" from touristy Stone Town. Bags of cloves sit alongside herbal cures for malaria and a DVD about the freemasons.
A short-bearded young information secretary, Said Amour, laments 48 years of failure and says that "political parties have failed so we are now taking over".
There are increasing signs that an unnerved government which has quietly banned many news outlets from covering Uamsho's activities, is preparing for a crackdown. Bonfires on the streets and deadly clashes with police returned over the last fortnight after Uamsho's spiritual leader Hadi Ahmed disappeared for four days. Popular online Swahili bulletin boards buzzed with accusations of state-sponsored assassination and thousands protested in Stone Town. Authorities vigorously denied any involvement in his disappearance. After a heavy deployment of police and troops, the cleric reappeared, claiming that he had been held by masked men who told him they were working with police.
Further protests followed after the preacher was arrested and then refused bail on Friday.
Meanwhile support for the enigmatic Uamsho shows no signs of waning.
In the mosques, supportive imams preach in favour of the "freedom fighters" of al-Shabaab, Islamic militants further up the coast in Somalia. Uamsho's critics are telling lies designed to destroy its reputation, warns Mr Amour, who says the people will not allow that to happen.
"Give a dog a bad name and then kill it," he repeats several times.