The outcome of this quarrel will decide who - the son or the daughter - is the suitable heir to Zulfikar Ali Bhutto, the charismatic populist who was overthrown as prime minister in 1977 and hanged two years later by the generals. Until now, the mantle has gone undisputedly to Ms Bhutto.
A sharp-willed woman, now 40, Ms Bhutto stuck it out in Pakistan after her father's death. Trapped for four years in jail, then banished abroad, she returned in 1988 and pieced together the fragments of her father's Pakistan People's Party (PPP), which had been shattered by mass arrests during the military regime.
That same year, she led her party to victory, and was poised to do it again this October.
Her leading opponent, Nawaz Sharif, the ex-prime minister, has lost backing from the strict religious parties which helped him win in 1990, while his own Pakistan Muslim League lies fractured by dissent.
But Ms Bhutto's brother has popped up. In a Muslim, male-dominated society like Pakistan's, it is usually the son who automatically gets the inheritance. This applies to land, money and political machines. 'He walks like his father and talks like him. I couldn't believe the resemblance,' said one journalist who saw him recently.
Speaking by telephone from Damascus, Mr Bhutto told journalists that he intended to run as an independent candidate for seven national assembly seats and 17 provincial seats in Sindh, the traditional Bhutto fiefdom. Asked why he was fighting against his sister's party, he replied: 'I don't see eye to eye with any of the parties that exist in Pakistan, and I don't want to be associated with any of the tactical steps that the PPP took . . . '
To complicate this family drama even more, Zulfikar's influential widow, Nusrat, announced earlier this month that she would assist her son's election campaign, even though she is chairwoman of Ms Bhutto's party. And, in a move of both practical and symbolic significance, Nusrat Bhutto is letting Mr Bhutto's election team take over her mansions in Karachi and at the ancestral homestead at Larkana, in Sindh, which were Ms Bhutto's campaign fortresses.
As the election nears, baffled party members are trying to work out why Nusrat Bhutto is not helping her daughter more. Some say she wants to see her only living son (her other son, Shahnawaz, was murdered in 1985) restored to eminence in Pakistan and have the terrorist charges against him dropped. Others say that she also wants Mr Bhutto to parry the growing influence of Asif Zardari, Ms Bhutto's husband, who is filling the top party posts with his cronies.
'Murtaza may arrive before, during or after the elections. He could come at any moment,' said his Karachi spokesman, Subak Majeed. If so, Mr Bhutto will probably be arrested and taken straight to jail. It is not known whether he would be released on bail and allowed to campaign. He faces at least 12 charges, ranging from murder to air piracy, which date from the early 1980s, when he was leader of the terrorist al-Zulfikar organisation, which sought revenge against Pakistan's army generals for killing his father. Mr Bhutto arranged for a few young party loyalists to be trained by the pro-Soviet Kabul regime, but it is not clear how much command he exerted over these hotheads, who went back to Pakistan, committed a few blundering terrorist acts and were caught and killed. The generals used al-Zulfikar as a bogey-man to arrest more than 20,000 people, most of them Ms Bhutto's supporters.
Mr Bhutto is hoping that the present neutral caretaker government, led by the Prime Minister, Moeen Qureshi, will give him an amnesty or at least a fair trial. If acquitted, he would then keep whichever assembly seat he won.
Of the two siblings, Ms Bhutto is the more pragmatic and politically astute. She has learnt the art of compromise; Mr Bhutto is more impulsive. While Ms Bhutto opted for civil protest when her father was hanged, Mr Bhutto, who was then 26 and a student of literature at Oxford, decided to take up arms against the mighty Pakistan army. 'Even as a teenager,' wrote the Pakistani magazine Newsline recently, 'Murtaza Bhutto would pitch a tent in the backyard and play Che Guevara with his younger brother, Shahnawaz. His father's death turned these politically loaded childhood games into harsh reality.'
Ms Bhutto has not commented on her brother's possible return, other than to say it is a private family matter. But Mr Bhutto has accused his sister and their party lieutenants of spreading the rumour that his comeback is being staged by the country's powerful intelligence services. 'It's a complete fallacy. It originates from (their) fear, confusion.'
A senior PPP official, Salman Taseer, suggested Ms Bhutto's main rival, Mr Sharif, the ex-prime minister, and her foes in the military establishment want 'to use Murtaza to give the PPP an extremist image, and then they want him to split the party'.