Danny Devine has left Inverness Caledonian Thistle to join Partick Thistle, who have also signed fellow defender David Syme.
The 18-year-old Syme, who has agreed a one-year contract, had been transfer-listed by Kilmarnock.
Devine signed for two years after three seasons with Caley Thistle.
Inverness manager Richie Foran said of the Northern Irish 23-year-old: "We made Danny our best offer to extend his stay with us in the Highlands."
Devine, who joined Caley Thistle after leaving Fleetwood Town, was a near ever-present last season, playing 45 times.
Midfielders Danny Williams and James Vincent had also rejected new contracts and accepted offers from top-flight rivals Dundee before Foran succeeded John Hughes as manager.
Striker Miles Storey, who had been on loan from Swindon Town, preferred to join Aberdeen on a permanent contract.
However, Foran has strengthened his attacking options by signing Scott Boden after the striker left Newport County.
The arrival of Devine and Syme at Firhill means that Thistle have signed three players in two days, with striker Ade Azeez having agreed a switch from Wimbledon to Glasgow.
Dundee United midfielder Chris Erskine has previously announced that he will be returning to Maryhill for a third stint after signing a pre-contract earlier this year.
Syme made six appearances for Kilmarnock in the last campaign, but his season was cut short by injury in January and he did not play under Lee Clark after the Englishman succeeded Gary Locke as manager.
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