Suppose two countries. Let's call them A and B.
Suppose, for simplicity, that the exchange rate between these two countries is 1. Further, suppose both countries have the same inflation rate and same nominal interest rate (and thus the same real interest rate).
Now, suppose that country A, for whatever reason, triggers a contractionary monetary policy. The central bank of country A enacts this policy by selling securities in the open market. These securities sells cause a sharp increase in supply of securities. Given a relatively inelastic demand, this forces securities prices downs and yields up. That is to say - this action causes interest rates to rise. A rising interest rate is considered contractionary because it slows investment.
So now we have two countries, A and B, with a 1:1 exchange rate but now country A has a higher real interest rate than does country B. Assume it cost nothing for people in country B to invest in securities in country A.
We can reasonably expect people in country B, facing a 1:1 fixed exchange rate and no cost of moving capital, to buy Country A securities. Why? Because the securities in country A are more profitable because they offer a higher yield. That is to say - they are more profitable because of the higher prevailing interest rate in country A.
So, contractionary policy in country A raised interest rates (to slow investment). This interest rate hike made securities in country A more profitable than they were before the interest rate hike. This increase in the profitability in the securities of country A induced investments from people in Country B.
Hopefully that helps.