Police believe a house fire in Doubleview and a stabbing in Watermans Bay last night are linked.
Police were called to an incident in West Coast Drive about 8.15pm and found a seriously injured 33-year-old man.
The man was taken to Royal Perth Hospital with multiple stab wounds.
About two hours later, two people ran from a fire in partially constructed house in Doubleview.
Firefighters and police were called to the Flamborough Street property just before 10pm.
Someone was reportedly trying to burn down the house.
Police said two people in the house fled before the fire took hold.
The blaze started on the ground floor of the two-storey house and spread upstairs.
Four crews extinguished the blaze by 10.40pm, but it caused $150,000 worth of damage.
Arson squad detectives are currently investigating both incidents and believe they are related.
A man is currently assisting police in relation to both incidents.
The 33-year-old man remains in hospital in a stable condition.